Activated forms of notch and methods based thereon

ABSTRACT

The present invention is directed to methods for detecting or measuring Notch activation by observing or measuring the appearance of Notch on the cell surface or by observing or measuring Notch cleavage products that are indicative of Notch activation. The present invention is also directed to methods for detecting a molecule that modulates Notch activation by observing or measuring a change in the amount of Notch expressed on the cell surface or a change in the amount or pattern of Notch cleavage products. The present invention is also directed to a substantially purified activated heterodimeric form of Notch and components thereof and pharmaceutical compositions and kits thereof. The present invention is based, at least in part, on the discovery that Notch in its active form, i.e., the form that mediates signal transduction and that binds Notch ligands such as Delta, is a heterodimer of an about 180 kDa subunit (N EC ) and an about 110 kDa subunit (N TM ), which are tethered together through a reducing agent-sensitive linkage, in particular, a non-covalent, metal ion-dependent linkage.

This application is a continuation-in-part application of U.S. application Ser. No. 08/899,232 filed Jul. 23, 1997, now U.S. Pat. No. 6,436,650, which is incorporated herein in its entirety.

This invention was made with government support under grant number NS 26084 awarded by the National Institutes of Health. The government has certain rights in the invention.

1. FIELD OF THE INVENTION

The present invention is directed to methods for detecting or measuring Notch activation by observing or measuring the appearance of Notch on the cell surface or by observing or measuring Notch cleavage products that are indicative of Notch activation. The present invention is also directed to methods for detecting a molecule that modulates Notch activation by observing or measuring a change in the amount of Notch expressed on the cell surface or a change in the amount or pattern of Notch cleavage products. The present invention is also directed to a substantially purified activated heterodimeric form of Notch and pharmaceutical compositions and kits thereof.

2. BACKGROUND OF THE INVENTION

Genetic and molecular studies have led to the identification of a group of genes which define distinct elements of the Notch signaling pathway. While the identification of these various elements has come exclusively. from Drosophila using genetic tools as the initial guide, subsequent analyses have lead to the identification of homologous proteins in vertebrate species including humans. FIG. 1 depicts the molecular relationships between the known Notch pathway elements as well as their subcellular localization (Artavanis-Tsakonas et al., 1995, Science 268:225-232).

The Drosophila Notch gene encodes an ˜300 kD transmembrane protein that acts as a receptor in a cell-cell signaling mechanism controlling cell fate decisions throughout development (reviewed, e.g., in Artavanis-Tsakonas et al., 1995, Science 268:225-232). Closely related homologs of Drosophila Notch have been isolated from a number of vertebrate species, including humans, with multiple paralogs representing the single Drosophila gene in vertebrate genomes. The isolation of cDNA clones encoding the C-terminus of a human Notch paralog, originally termed hN, has been reported (Stifani et al., 1992, Nature Genetics 2:119-127). The encoded protein is designated human Notch2 because of its close relationship to the Notch2 proteins found in other species (Weinmaster et al., 1992, Development 116:931-941). The hallmark Notch2 structures are common to all the Notch-related proteins, including, in the extracellular domain, a stretch of 34 to 36 tandem Epidermal Growth Factor-like (EGF) repeats and three Lin-12/Notch repeats (LN repeats), and, in the intracellular domain, 6 Ankyrin repeats and a PEST-containing region. Like Drosophila Notch and the related C. elegans genes lin-12 and glp-1 (Sternberg, 1993, Current Biology 3:763-765; Greenwald, 1994, Current Opinion in Genetics and Development 4:556-562), the vertebrate Notch homologs play a role in a variety of developmental processes by controlling cell fate decisions (reviewed, e.g., in Blaumueller and Artavanis-Tsakonas, 1997, Persp. on Dev. Neurobiol. 4:325-343). (For further human Notch sequences, see International Publication WO 92/19734.)

The extracellular domain of Notch carries 36 Epidermal Growth Factor-like (EGF) repeats, two of which (repeats 11 and 12) have been implicated in interactions with the Notch ligands Serrate and Delta. Delta and Serrate are membrane bound ligands with EGF homologous extracellular domains, which interact physically with Notch on adjacent cells to trigger signaling.

Functional analyses involving the expression of truncated forms of the Notch receptor have indicated that receptor activation depends on the six cdc10/ankyrin repeats in the intracellular domain. Deltex and Suppressor of Hairless, whose over-expression results in an apparent activation of the pathway, associate with those repeats.

Deltex is a cytoplasmic protein which contains a ring zinc finger. Suppressor of Hairless on the other hand, is the Drosophila homologue of CBF1, a mammalian DNA binding protein involved in the Epstein-Barr virus-induced immortalization of B cells. It has been demonstrated that, at least in cultured cells, Suppressor of Hairless associates with the cdc10/ankyrin repeats in the cytoplasm and translocates into the nucleus upon the interaction of the Notch receptor with its ligand Delta on adjacent cells (Fortini and Artavanis, 1994, Cell 79:273-282). The association of Hairless, a novel nuclear protein, with Suppressor of Hairless has been documented using the yeast two hybrid system; therefore, it is believed that the involvement of Suppressor of Hairless in transcription is modulated by Hairless (Brou et al., 1994, Genes Dev. 8:2491; Knust et al. 1992, Genetics 129:803).

Finally, it is known that Notch signaling results in the activation of at least certain basic helix-loop-helix (bHLH) genes within the Enhancer of Split complex (Delidakis et al., 1991, Genetics 129:803). Mastermind encodes a novel ubiquitous nuclear protein whose relationship to Notch signaling remains unclear but is involved in the Notch pathway as shown by genetic analysis (Smoller et al., 1990, Genes Dev. 4:1688).

The generality of the Notch pathway manifests itself at different levels. At the genetic level, many mutations exist which affect the development of a very broad spectrum of cell types in Drosophila. Knockout mutations in mice are embryonic lethals consistent with a fundamental role for Notch function (Swiatek et al., 1994, Genes Dev. 8:707). Mutations in the Notch pathway in the hematopoietic system in humans are associated with lymphoblastic leukemia (Ellison et al., 1991, Cell 66:649-661). Finally the expression of mutant forms of Notch in developing Xenopus embryos interferes profoundly with normal development (Coffman et al., 1993, Cell 73:659). Increased level of Notch expression is found in some malignant tissue in humans (International Publication WO 94/07474).

The expression patterns of Notch in the Drosophila embryo are complex and dynamic. The Notch protein is broadly expressed in the early embryo, and subsequently becomes restricted to uncommitted or proliferative groups of cells as development proceeds. In the adult, expression persists in the regenerating tissues of the ovaries and testes (reviewed in Fortini et al., 1993, Cell 75:1245-1247; Jan et al., 1993, Proc. Natl. Acad. Sci. USA 90:8305-8307; Sternberg, 1993, Curr. Biol. 3:763-765; Greenwald, 1994, Curr. Opin. Genet. Dev. 4:556-562; Artavanis-Tsakonas et al., 1995, Science 268:225-232). Studies of the expression of Notch1, one of three known vertebrate homologs of Notch, in zebrafish and Xenopus, have shown that the general patterns are similar; with Notch expression associated in general with non-terminally differentiated, proliferative cell populations. Tissues with high expression levels include the developing brain, eye and neural tube (Coffman et al., 1990, Science 249:1438-1441; Bierkamp et al., 1993, Mech. Dev. 43:87-100). While studies in mammals have shown the expression of the corresponding Notch homologs to begin later in development, the proteins are expressed in dynamic patterns in tissues undergoing cell fate determination or rapid proliferation (Weinmaster et al., 1991, Development 113:199-205; Reaume et al., 1992, Dev. Biol. 154:377-387; Stifani et al., 1992, Nature Genet. 2:119-127; Weinmaster et al., 1992, Development 116:931-941; Kopan et al., 1993, J. Cell Biol. 121:631-641; Lardelli et al., 1993, Exp. Cell Res. 204:364-372; Lardelli et al., 1994, Mech. Dev. 46:123-136; Henrique et al., 1995, Nature 375:787-790; Horvitz et al., 1991, Nature 351:535-541; Franco del Amo et al., 1992, Development 115:737-744). Among the tissues in which mammalian Notch homologs are first expressed are the pre-somitic mesoderm and the developing neuroepithelium of the embryo. In the pre-somitic mesoderm, expression of Notch1 is seen in all of the migrated mesoderm, and a particularly dense band is seen at the anterior edge of pre-somitic mesoderm. This expression has been shown to decrease once the somites have formed, indicating a role for Notch in the differentiation of somatic precursor cells (Reaume et al., 1992, Dev. Biol. 154:377-387; Horvitz et al., 1991, Nature 351:535-541). Similar expression patterns are seen for mouse Delta (Simske et al., 1995, Nature 375:142-145).

Within the developing mammalian nervous system, expression patterns of Notch homologue have been shown to be prominent in particular regions of the ventricular zone of the spinal cord, as well as in components of the peripheral nervous system, in an overlapping but non-identical pattern. Notch expression in the nervous system appears to be limited to regions of cellular proliferation, and is absent from nearby populations of recently differentiated cells (Weinmaster et al., 1991, Development 113:199-205; Reaume et al., 1992, Dev. Biol. 154:377-387; Weinmaster et al., 1992, Development 116:931-941; Kopan et al., 1993, J. Cell Biol. 121:631-641; Lardelli et al., 1993, Exp. Cell Res. 204:364-372; Lardelli et al., 1994, Mech. Dev. 46:123-136; Henrique et al., 1995, Nature 375:787-790; Horvitz et al., 1991, Nature 351:535-541). A rat Notch ligand is also expressed within the developing spinal cord, in distinct bands of the ventricular zone that overlap with the expression domains of the Notch genes. The spatio-temporal expression pattern of this ligand correlates well with the patterns of cells committing to spinal cord neuronal fates, which demonstrates the usefulness of Notch as a marker of populations of cells for neuronal fates (Henrique et al., 1995, Nature 375:787-790). This has also been suggested for vertebrate Delta homologs, whose expression domains also overlap with those of Notch1 (Larsson et al., 1994, Genomics 24:253-258; Fortini et al., 1993, Nature 365:555-557; Simske et al., 1995, Nature 375:142-145). In the cases of the Xenopus and chicken homologs, Delta is actually expressed only in scattered cells within the Notch1 expression domain, as would be expected from the lateral specification model, and these patterns “foreshadow” future patterns of neuronal differentiation (Larsson et al., 1994, Genomics 24:253-258; Fortini et al., 1993, Nature 365:555-557).

Other vertebrate studies of particular interest have focused on the expression of Notch homologs in developing sensory structures, including the retina, hair follicles and tooth buds. In the case of the Xenopus retina, Notch1 is expressed in the undifferentiated cells of the central marginal zone and central retina (Coffman et al., 1990, Science 249:1439-1441; Mango et al., 1991, Nature 352:811-815). Studies in the rat have also demonstrated an association of Notch1 with differentiating cells in the developing retina have been interpreted to suggest that Notch1 plays a role in successive cell fate choices in this tissue (Lyman et al., 1993, Proc. Natl. Acad. Sci. USA 90:10395-10399).

A detailed analysis of mouse Notch1 expression in the regenerating matrix cells of hair follicles was undertaken to examine the potential participation of Notch proteins in epithelial/mesenchymal inductive interactions (Franco del Amo et al., 1992, Development 115:737-744). Such a role had originally been suggested for Notch1 based on its expression in rat whiskers and tooth buds (Weinmaster et al., 1991, Development 113:199-205). Notch1 expression was instead found to be limited to subsets of non-mitotic, differentiating cells that are not subject to epithelial/mesenchymal interactions, a finding that is consistent with Notch expression elsewhere.

Expression studies of Notch proteins in human tissue and cell lines have also been reported. The aberrant expression of a truncated Notch1 RNA in human T-cell leukemia results from a translocation with a breakpoint in Notch1 (Ellisen et al., 1991, Cell 66:649-661). A study of human Notch1 expression during hematopoiesis has suggested a role for Notch1 in the early differentiation of T-cell precursors (Mango et al., 1994, Development 120:2305-2315). Additional studies of human Notch1 and Notch2 expression have been performed on adult tissue sections including both normal and neoplastic cervical and colon tissue. Notch1 and Notch2 appear to be expressed in overlapping patterns in differentiating populations of cells within squamous epithelia of normal tissues that have been examined and are clearly not expressed in normal columnar epithelia, except in some of the precursor cells. Both proteins are expressed in neoplasias, in cases ranging from relatively benign squamous metaplasias to cancerous invasive adenocarcinomas in which columnar epithelia are replaced by these tumors (Mello et al., 1994, Cell 77:95-106).

Insight into the developmental role and the general nature of Notch signaling has emerged from studies with truncated, constitutively activated forms of Notch in several species. These recombinantly engineered Notch forms, which lack extracellular ligand-binding domains, resemble the naturally occurring oncogenic variants of mammalian Notch proteins and are constitutively activated using phenotypic criteria (Greenwald, 1994, Curr. Opin. Genet. Dev. 4:556; Fortini et al., 1993, Nature 365:555-557; Coffman et al., 1993, Cell 73:659-671; Struhl et al., 1993, Cell 69:1073; Rebay et al., 1993, Cell 74: 319-329; Kopan et al., 1994, Development 120:2385; Roehl et al., 1993, Nature 364:632).

Ubiquitous expression of activated Notch in the Drosophila embryo suppresses neuroblast segregation without impairing epidermal differentiation (Struhl et al., 1993, Cell 69:331; Rebay et al., 1993, Cell 74:319-329).

Persistent expression of activated Notch in developing imaginal epithelia likewise results in an overproduction of epidermis at the expense of neural structures (Struhl et al., 1993, Cell 69:331).

Neuroblast segregation occurs in temporal waves that are delayed but not prevented by transient expression of activated Notch in the embryo (Struhl et al., 1993, Cell 69:331).

Transient expression in well-defined cells of the rosophila eye imaginal disc causes the cells to ignore their normal inductive cues and to adopt alternative cell fates (Fortini et al., 1993, Nature 365:555-557).

Studies utilizing transient expression of activated Notch in either the Drosophila embryo or the eye disc indicate that once Notch signaling activity has subsided, cells may recover and differentiate properly or respond to later developmental cues (Fortini et al., 1993, Nature 365:555-557; Struhl et al., 1993, Cell 69:331).

For a general review on the Notch pathway and Notch signaling, see Artavanis-Tsakonas et al., 1995, Science 268:225-232.

Ligands, cytoplasmic effectors and nuclear elements of Notch signaling have been identified in Drosophila, and vertebrate counterparts have also been cloned (reviewed in Artavanis-Tsakonas et al., 1995, Science 268:225-232). While protein interactions between the various elements have been documented, the biochemical nature of Notch signaling remains elusive. Expression of truncated forms of Notch reveal that Notch proteins without transmembrane and extracellular domains are translocated to the nucleus both in transgenic flies and in transfected mammalian or Drosophila cells (Lieber et al., 1993, Genes and Development 7:1949-1965; Fortini et al., 1993, Nature 365:555-557; Ahmad et al., 1995, Mechanisms of Development 53:78-85; Zagouras et al., 1995, Proc. Natl. Acad. Sci. USA 92:6414-6418). Sequence comparisons between mammalian and Drosophila Notch molecules, along with deletion analysis, have found two nuclear localization sequences that reside on either side of the Ankyrin repeats (Stifani et al., 1992, Nature Genetics 2:119-127; Lieber et al., 1993, Genes and Development 7:1949-1965; Kopan et al., 1994, Development 120:2385-2396). These findings prompted the speculation that Notch may be directly participating in nuclear events by means of a proteolytic cleavage and subsequent translocation of the intracellular fragment into the nucleus. However, conclusive functional evidence for such a hypothesis remained elusive (Artavanis-Tsakonas et al., 1995, Science 268:225-232) until the disclosure of Schroeter et al., 1998, Nature 393:382-386. Schroeter et al. demonstrated that Notch1, upon ligand binding, is cleaved between amino acid G1743 and V1744 releasing the intracellular domain. The released intracellular domain translocates into the nucleus, and through interaction with members of the CSL (CBF-1, Su(H), Lag-1) family of DNA binding proteins, activates transcription.

In a separate study, Logeat et al., 1998, Proc. Natl. Acad. Sci. USA 95:8108-8112 (Logeat et al.), have demonstrated that human Notch1 is constitutively cleaved by the convertase furin at the carboxyl side of the sequence ArgGlnArgArg (amino acids 1651-1654), which sequence is located between the transmembrane domain and the Lin-12/Notch repeats. The cleavage of Notch1 by furin results in the cell surface expression of a heterodimeric functional receptor.

Citation or identification of any reference in Section 2 or any other section of this application shall not be construed as an admission that such reference is available as prior art to the present invention.

3. SUMMARY OF THE INVENTION

The present invention is directed to methods for detecting or measuring Notch activation by observing or measuring the appearance of Notch on the cell surface or by observing or measuring Notch cleavage products that are indicative of Notch activation. In one aspect of this embodiment of the invention, the method for detecting or measuring Notch activation in a cell comprises detecting or measuring the expression of Notch on the surface of said cell, wherein the presence and amount of Notch on the surface indicates the presence and amount, respectively, of Notch activation. In another aspect, the method comprises detecting or measuring the expression of one or more Notch cleavage products selected from the group consisting of N^(EC) and N^(TM). In yet another aspect, the method comprises detecting or measuring one or more fragments of Notch selected from the group consisting of an amino-terminal fragment of full-length Notch terminating between the epidermal growth factor-like repeat domain and the transmembrane domain (in particular, between the Lin-12/Notch repeats and the transmembrane domain) of full-length Notch, and a carboxy-terminal fragment of full-length Notch with its amino terminus situated between the epidermal growth factor-like repeat domain and the transmembrane domain (in particular, between the Lin-12/Notch repeats and the transmembrane domain), or detecting or measuring one or more fragments of Notch selected from the group consisting of Notch fragments having a molecular weight of about 270, 200, 170, 140, 110, 100, 90 and 85 kilodaltons. In yet another aspect, the method comprises detecting or measuring a Notch heterodimer containing a reducing agent-sensitive linkage, in particular, a non-covalent, metal ion-dependent (e.g., calcium ion-dependent) linkage.

The present invention is based, at least in part, on the discovery that Notch in its active form, i.e., the form that mediates signal transduction and that binds Notch ligands such as Delta, is a heterodimer of two Notch cleavage products, an about (±10%) 180 kilodaltons (kDa) subunit (N^(EC)) and an about (±10%) 110 kDa subunit (N^(TM)), which are tethered together through a reducing agent-sensitive linkage, in particular, a non-covalent, metal ion-dependent (e.g., calcium ion-dependent) linkage. Full length Notch is not expressed on the cell surface and is ligand inaccessible. As shown by way of example infra, the two subunits arise due to a proteolytic cleavage of the full length Notch molecule in the trans-Golgi at a site in Notch amino-terminal to the transmembrane domain and carboxy-terminal to the EGF repeat region, thus generating an extracellular fragment (N^(EC)) of about 180 kDa and a transmembrane/intracellular fragment (N^(TM)) of about 110 kDa. The detection of full length Notch and of Notch cleavage products, as well as Notch that is present on the cell surface, can be carried out by methods well known to those of skill in the art, e.g., precipitation or binding to an immobilized binding partner (e.g., on a plate or column), e.g., anti-Notch antibodies or ligands of Notch, such as Delta and Serrate.

The detection or measurement of Notch activation is important in the study and manipulation of differentiation processes, since Notch plays a key role in cell fate (differentiation) determination. Also, disorders of cell fate, in particular hyperproliferative (e.g., cancer) or hypoproliferative disorders, involving aberrant or undesirable levels of active Notch expression can be diagnosed or screened for by detecting such active Notch expression, as described more fully infra. Molecules that modulate Notch function are important tools for studying and manipulating differentiation processes, e.g., in expanding cell populations without substantial differentiation (International Publication WO 97/11716), in cancer studies and therapy (International Publication WO 94/07474), and differentiation studies on normal tissue.

In another embodiment, the present invention is also directed to methods for identifying a molecule that modulates Notch activation by detecting or measuring a change in the amount of Notch expressed on the cell surface or a change in the amount or pattern of Notch cleavage products. In one aspect of this embodiment of the invention, the method for identifying a modulator of Notch activation comprises providing a cell with a candidate modulator molecule and detecting or measuring the amount of Notch on the surface of the cell, in which a difference in the presence or amount compared to a cell not contacted with the candidate molecule indicates that the candidate molecule modulates Notch activation. In another aspect, the method for identifying a modulator of Notch activation comprises providing a cell with a candidate modulator molecule and detecting or measuring the expression by the cell of one or more Notch cleavage products selected from the group consisting of N^(EC) and N^(TM), in which a difference in the presence or amount of said one or more cleavage products compared to a Notch cell not contacted with the candidate molecule indicates that the molecule modulates Notch activity.

In an alternative aspect, the method for identifying a modulator of Notch activation comprises contacting a candidate modulator molecule with a full length Notch in the presence of a composition comprising cellular proteins, under conditions conducive to cleavage of the full-length Notch by one or more components of the composition and detecting or measuring the amount of Notch cleavage products N^(EC) and N^(TM) that result, in which a difference in the presence or amount of said Notch cleavage products compared to a full-length Notch in presence of said composition not contacted with the candidate molecule indicates that the molecule modulates Notch activity.

The present invention is also directed to a substantially purified active form of Notch which comprises Notch fragments tethered together through a reducing agent-sensitive linkage, particularly, a non-covalent, metal ion-dependent linkage, and pharmaceutical compositions and kits thereof.

4. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic diagram of the Notch signaling pathway. The Notch receptor can bind to either Delta or Serrate through its extracellular domain. Ligand binding can result in receptor multimerization that is stabilized by interactions between the intracellular ankyrin repeats of Notch and the cytoplasmic protein Deltex. These events can control the nuclear translocation of the DNA-binding protein Suppressor of Hairless and its known association with the Hairless protein. The transcriptional induction of the Enhancer of Split basic helix-loop-helix (bHLH) genes appears to depend on Notch signaling.

FIGS. 2A-2D depict is a Notch homolog sequence comparison. The human Notch2 (humN2) (SEQ ID NO:1), human Notch1 (humN1) (SEQ ID NO:2), Xenopus Notch/Xotch (XenN) (SEQ ID NO:3), and Drosophila Notch (DrosN) (SEQ ID NO:4) protein sequences are aligned, with names indicated to the left and numbering to the right (Wharton et al., 1985, Cell 43:567-581; Coffman et al., 1990, Science 249:1438-1441; Ellisen et al., 1991, Cell 66:649-661; Stifani et al., 1992, Nature Genetics 2:119-127). Major Notch protein motifs are enclosed in boxes. Starting from the N-terminal, the boxed regions indicate: EGF repeats, Lin-12/Notch (LN) repeats, transmembrane domain (TM), Ankyrin repeats, and PEST-containing region. Also indicated are the putative CcN motif components (Stifani et al., 1992, Nature Genetics 2:119-127) nuclear localization signal (NLS, BNTS) and putative CKII and cdc2 phosphorylation sites. The calculated signal cleavage site is indicated with an arrow.

FIGS. 3A-3E are Western blot analyses of human cell lines, human tissues, Drosophila cell lines, rat and Drosophila embryos. The cell source of each lysate is indicated above the lanes. Notch2 expression was monitored with antibody bhN6D and Notch1 expression with antibody bTAN20. Both recognize intracellular epitopes of the protein (Zagouras et al., 1995, Proc. Natl. Acad. Sci. USA 92:6414-6418). FIGS. 3A and 3B show Notch2 expression. FIGS. 3C and 3D show Notch1 expression. FIG. 3E shows the expression of Drosophila Notch in embryos, Drosophila KC cultured cells, which endogenously express Notch, and Drosophila S2 cells, which do not endogenously express Notch but have been stably transfected with a Notch expression vector. The antibody used (9C6) recognizes an intracellular epitope (Fehon et al., 1990, Cell 61:523-534). In all the panels the 110 kDa major breakdown product (N^(TM)) and the position of the full-length Notch protein are indicated. Molecular weight markers are shown on the left of each panel.

FIG. 4 shows the subcellular location of the 110 kDa (N^(TM)) fragment. Subcellular fractionation of SJ-NB5 cells followed by SDS-PAGE and Western blot with a Notch2 antibody raised against an intracellular epitope (bhN6D). Whole cell lysate is shown on the left lane. This lysate was centrifuged at 900×g and the pellet (0.9K) is in the second lane. This pellet was resuspended and analyzed on a sucrose step gradient at 0%, 40% and 50% sucrose. The pellet of the gradient, which contains the nuclei (NP), and the interphases are analyzed as indicated in the last three lanes. The supernatant of the initial low spin was centrifuged at 40,000×g and the pellet was analyzed in the lane indicated as 40K. Finally the supernatant of the 40K spin was centrifuged again at 100,000×g (lanes indicated as 100K) and the resulting pellet (P) and supernatant (S) were loaded on the gel.

FIG. 5 shows that the 110 kDa (N^(TM)) fragment is expressed on the cell surface. SJ-NB5 cells were treated with biotin (+Biotin) while control cells were not (−Biotin). Each sample was lysed and divided into three equal portions precipitated with immobilized streptavidin, anti-Notch2 antibody PGHN (lanes 1, 2 and 3) or normal rabbit serum (lanes 4, 5 and 6). Samples were run on a 4-20% SDS-PAGE gel and blotted with antibody bhN6D. Molecular weight markers are shown on the left. N^(TM) accumulates on the surface, while full-length Notch is not precipitated by streptavidin.

FIGS. 6A-6B show that the processing of Notch2 is blocked by Brefeldin A and at 19° C. FIG. 6A shows the results of a pulse labeling experiment in SJ-NB5 cells in the presence or absence of Brefeldin A. [³⁵S]-Methionine was allowed to incorporate for 20 minutes and then chased for 0, 15, 30, 45, 60, 90 minutes at 37° C. The cell lysates were immunoprecipitated by PGHN (a polyclonal antibody raised against intracellular Notch2 epitopes, Zagouras et al., 1995, Proc. Natl. Acad. Sci. USA 92:6414-6418), analyzed by SDS-PAGE and followed by fluorography. FIG. 6B shows SJ-NB5 cells labeled with [³⁵S]-methionine for 20 minutes, chased either at 37° C. or 19° C. for 0, 30, 60, 90 minutes, immunoprecipitated by PGHN and analyzed by SDS-PAGE, followed by fluorography. Two fragments accumulate during the chase and co-immunoprecipitate with PGHN: a 180 kDa fragment (N^(EC)) and a 110 kDa fragment (N^(TM)).

FIG. 7 shows that full-length Notch does not accumulate on the cell surface. SJ-NB5 cells were pulse labeled with [³⁵S]-methionine for 10 minutes, chased for 0, 15, 30, 45, 60, 90 and 120 minutes, and this was followed by the biotinylation of the surface proteins. The cell lysates were immunoprecipitated with the polyclonal Notch2 antibody PGHN (Zagouras et al., 1995, Proc. Natl. Acad. Sci. USA 92:6414-6418). Lanes corresponding to those lysates are designated T and show all the antigens recognized by PGHN. At each time point, part of the PGHN immunoprecipitate was resuspended and then immunoprecipitated by streptavidin, which would correspond to the Notch antigens on the surface (S lanes). The immunoprecipitation products were analyzed by SDS-PAGE followed by fluorography. The accumulation of the N^(TM) and N^(EC) fragments is evident, while full-length Notch is not detected on the surface.

FIG. 8 shows that Delta binds to the heterodimeric form of Notch. Identical amounts of cell lysates were precipitated with Delta antibodies from S2 cells expressing Notch (lane 1), S2 cells expressing Delta (lane 2), Notch and Delta expressing cells after one hour of aggregation (lane 3) and Notch and Delta expressing cells after two hours of aggregation (lane 4). In addition, a cell lysate of Notch expressing cells which had not been incubated with Delta antibody is shown in lane 5. All lanes are visualized with Notch antibody 9C6, which recognizes intracellular epitopes. The 110 kd Notch N^(TM) fragment is immunoprecipitated by the Delta antibodies in the extracts from Notch/Delta cell aggregates.

FIG. 9 is a model for the trafficking of the Notch receptor. Full-length Notch is synthesized in the ER (N) and then cleaved in the trans-Golgi network (TGN) extracellular region, producing two fragments, N^(TM) and N^(EC). Full-length Notch (N) reflects an inactive, presumably newly synthesized form of the receptor, which is not seen on the surface. N^(TM) and N^(EC), produced by a cleavage in the extracellular domain, are tethered together on the surface via a DTT-sensitive link, constituting the active form of the receptor that can interact with ligands (horizontally lined circle) and/or interact homotypically with another Notch receptor or conceivably with other surface molecules.

FIGS. 10A-10B are Western blot analyses showing the Notch cleavage pattern in human cells, in Drosophila embryo extracts and in Drosophila S2 cells which recombinantly express Notch. FIG. 10A is a Western blot of SJ-NB5 cells (human neuroblastoma) using antibody bhN6D and FIG. 10B is a Western blot of Drosophila embryo extracts and in Drosophila S2 cells which recombinantly express Notch using antibody 9C6. Molecular weight markers are indicated at left for both FIGS. 10A and 10B.

FIGS. 11A-11B show that N^(EC) and N^(TM) are associated in a non-covalent manner. FIG. 11A is a Western blot analysis demonstrating that N^(EC) is present in the supernatant of Notch expressing S2 cells that have been resuspended in 2 mM EDTA, Tris-HCl saline buffer (EDTA), whereas in the presence of 2 mM CaCl₂ (Ca²⁺) insignificant amounts of N^(EC) are detected. FIG. 11B is a Western blot of a sucrose density centrifugation of S2 cell extracts that shows N^(EC) and N^(TM) co-sediment in the presence of CaCl₂, whereas N^(EC) and N^(TM) sediment separately in the presence of EDTA.

5. DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to methods for detecting or measuring Notch activation by observing or measuring the appearance of Notch on the cell surface or by observing or measuring Notch cleavage products, that are indicative of Notch activation. In one aspect of this embodiment of the invention, the method for detecting or measuring Notch activation in a cell comprises detecting or measuring the expression of Notch on the surface of said cell, wherein the presence and amount of Notch on the surface indicates the presence and amount, respectively, of Notch activation. In another aspect, the method comprises detecting or measuring the expression of one or more Notch cleavage products selected from the group consisting of N^(EC) and N^(TM). In yet another aspect, the method comprises detecting or measuring one or more fragments of Notch selected from the group consisting of an amino-terminal fragment of full-length Notch terminating between the epidermal growth factor-like repeat domain and the transmembrane domain (in particular, between the Lin-12/Notch repeats and the transmembrane domain) of full-length Notch, and a carboxy-terminal fragment of full-length Notch with its amino terminus situated between the epidermal growth factor-like repeat domain and the transmembrane domain (in particular, between the Lin-12/Notch repeats and the transmembrane domain), or detecting or measuring one or more fragments of Notch selected from the group consisting of Notch fragments having a molecular weight of about 270, 200, 170, 140, 110, 100, 90 and 85 kilodaltons. In yet another aspect, the method comprises detecting or measuring a Notch heterodimer containing a reducing agent-sensitive linkage, in particular, a non-covalent, metal ion-dependent (e.g., calcium ion-dependent) linkage.

The present invention is based, at least in part, on the discovery that Notch in its active form, i.e., the form that mediates signal transduction and that binds Notch ligands such as Delta, is a heterodimer of two Notch cleavage products, an about (±10%) 180 kilodaltons (kDa) subunit (N^(EC)) and an about (±10%) 110 kDa subunit (N^(TM)), which are tethered together through a reducing agent-sensitive linkage, in particular, a non-covalent, metal ion-dependent (e.g., calcium ion-dependent) linkage. Full length Notch is not expressed on the cell surface and is ligand inaccessible. As shown by way of example infra, the two subunits arise due to a proteolytic cleavage of the full length Notch molecule in the trans-Golgi at a site in Notch amino-terminal to the transmembrane domain and carboxy-terminal to the EGF repeat region, thus generating an extracellular fragment (N^(EC)) of about 180 kDa and a transmembrane/intracellular fragment (N^(TM)) of about 110 kDa. The detection of full length Notch and of Notch cleavage products, as well as Notch that is present on the cell surface, can be carried out by methods well known to those of skill in the art, e.g., precipitation or binding to an immobilized binding partner (e.g., on a plate or column), e.g., anti-Notch antibodies or ligands of Notch, such as Delta and Serrate.

Logeat et al., 1998, Proc. Natl. Acad. Sci. USA 95:8108-8112, demonstrated that the convertase furin cleaves human Notch1 on the carboxy side of the sequence ArgGlnArgArg (amino acids 1651-1654), which is in the region between the Lin-12/Notch repeats and the transmembrane domain. Although human Notch2, as well as mouse Notch (mNotch), do not have sequence identity at this region with human Notch1, we believe the cleavage site in these proteins likely to be between the epidermal growth factor-like repeats and the transmembrane domain, e.g., between the Lin-12/Notch repeats and the transmembrane domain.

The detection or measurement of Notch activation is important in the study and manipulation of differentiation processes, since Notch plays a key role in cell fate (differentiation) determination. Also, disorders of cell fate, in particular hyperproliferative (e.g., cancer) or hypoproliferative disorders, involving aberrant or undesirable levels of active Notch expression can be diagnosed or screened for by detecting such active Notch expression, as described more fully infra. Molecules that modulate Notch function are important tools for studying and manipulating differentiation processes, e.g., in expanding cell populations without substantial differentiation (International Publication WO 97/11716), in cancer studies and therapy (International Publication WO 94/07474), and differentiation studies on normal tissue.

In another embodiment, the present invention is also directed to methods for identifying a molecule that modulates Notch activation by detecting or measuring a change in the amount of Notch expressed on the cell surface or a change in the amount or pattern of Notch cleavage products. In one aspect of this embodiment of the invention, the method for identifying a modulator of Notch activation comprises providing a cell with a candidate modulator molecule and detecting or measuring the amount of Notch on the surface of the cell, in which a difference in the presence or amount compared to a cell not contacted with the candidate molecule indicates that the candidate molecule modulates Notch activation. In another aspect, the method for identifying a modulator of Notch activation comprises providing a cell with a candidate modulator molecule and detecting or measuring the expression by the cell of one or more Notch cleavage products selected from the group consisting of N^(EC) and N^(TM), in which a difference in the presence or amount of said one or more cleavage products compared to a Notch cell not contacted with the candidate molecule indicates that the molecule modulates Notch activity.

In an alternative aspect, the method for identifying a modulator of Notch activation comprises contacting a candidate modulator molecule with a full length Notch in the presence of a composition comprising cellular proteins, under conditions conducive to cleavage of the full-length Notch by one or more components of the composition and detecting or measuring the amount of Notch cleavage products N^(EC) and N^(TM) that result, in which a difference in the presence or amount of said Notch cleavage products compared to a full-length Notch in presence of said composition not contacted with the candidate molecule indicates that the molecule modulates Notch activity.

The present invention is also directed to a substantially purified active form of Notch which comprises Notch fragments tethered together through a reducing agent-sensitive linkage, in particular, a non-covalent, metal ion-dependent (e.g., calcium ion-dependent) linkage, and pharmaceutical compositions and kits thereof.

For clarity of disclosure, and not by way of limitation, the detailed description of the invention is divided into subsections, as follows.

5.1 Detection of the Active Form of Notch

In this embodiment of the invention, methods are provided for the detection or measuring of Notch activation comprising detecting or measuring the expression of Notch on the surface of said cell, wherein the presence and amount of Notch on the surface indicates the presence and amount, respectively, of Notch activation, or detecting or measuring the expression of one or more Notch cleavage products selected from the group consisting of N^(EC) and N^(TM), or detecting or measuring one or more fragments of Notch selected from the group consisting of an amino-terminal fragment of full-length Notch terminating between the epidermal growth factor-like repeat domain and the transmembrane domain (in particular, between the Lin-12/Notch repeats and the transmembrane domain) of full-length Notch repeats of full-length Notch, and a carboxy-terminal fragment with its amino terminus situated between the epidermal growth factor-like repeat domain and the transmembrane domain (in particular, between the Lin-12/Notch repeats and the transmembrane domain), or detecting or measuring one or more fragments of Notch selected from the group consisting of Notch fragments having a molecular weight of about 270, 200, 170, 140, 110, 100, 90 and 85 kilodaltons, or detecting or measuring a Notch heterodimer containing a reducing agent-sensitive linkage (particularly, a non-covalent, metal ion-dependent (e.g., calcium ion-dependent) linkage), or detecting or measuring a pattern of Notch fragments such as shown in FIG. 10A or 10B (with approximate molecular weights indicated on the right side of each figure). The assay methods of the invention are preferably carried out in vitro or in cell culture, but alternatively, may be carried out in vivo in an animal.

The invention is based, at least in part, on the discovery that the active form of Notch is not the full length form but rather a cell surface expressed heterodimer consisting of N^(EC) and N^(TM) Notch fragments tethered together through a reducing agent-sensitive linkage, in particular, a non-covalent, metal ion-dependent, (e.g., calcium ion-dependent) linkage.

In an alternative embodiment, methods are provided for the detecting or measuring of Notch activation comprising detecting or measuring the levels of N^(EC) in cell culture medium in the presence of an amount of a divalent metal ion chelator such as but not limited to EDTA or EGTA sufficient to cause dissociation of Notch surface heterodimers, wherein the presence and amount of Notch in the culture medium indicates the presence and amount, respectively, of Notch activation.

The ability to detect the expression of the active form of Notch is an important diagnostic/screening tool for cancer since Notch is known to be aberrantly expressed in neoplasias. For example, the aberrant expression of a truncated Notch1 RNA is seen in a human T cell leukemia (Ellison et al., 1991, Cell 66:649-661). Further, human Notch1 and Notch2 are not normally expressed in columnar epithelia but are expressed in neoplasias, in cases ranging from relatively benign squamous metaplasias to cancerous invasive adenocarcinomas in which columnar epithelia are replaced by these tumors (Mello et al., 1994, Cell 77:95-106; see also International Publication WO 94/07474). Therefore, using the assay methods of the present invention, aberrant forms or levels of Notch activation, which may be present in various malignancies, can be detected.

Any method known in the art for detecting or measuring the expression of Notch on the cell surface or the expression of Notch cleavage products indicative of Notch activation can be used. For example, and not by way of limitation, one such method of detection of the active form of Notch by detecting cell surface expression of Notch is by labeling generally the cell surface-expressed proteins with, e.g., biotin or ¹²⁵I, and then detecting the label on Notch. If no label is detected, Notch is not expressed on the cell surface, and thus the active form of Notch is not expressed. Another method of detection of the active form of Notch is, e.g., by labeling generally the cell surface-expressed proteins, with, e.g., biotin or ¹²⁵I, adding a sufficient amount of a divalent metal ion chelator to disrupt the interaction between N^(EC) and N^(TM), and then detecting the label in the cell culture medium. If no label is detected, the active form of Notch is not expressed. In a specific embodiment, Notch can be isolated using, e.g., an anti-Notch antibody or Notch ligand or a binding fragment of a Notch ligand, before detecting the label on Notch. A particular method of detecting cell surface Notch is to contact a labelled anti-Notch antibody, e.g., labeled with a fluorescent dye or with a radioactive isotope such as ¹²⁵I, to whole cells and then to detect cells having the label through, e.g., flow cytometry, fluorescent activated cell sorting (FACS) analysis, or scintillation counting.

Another method is to detect the active form of Notch by detecting one or more Notch cleavage products selected from the group consisting of N^(EC) and N^(TM), or selected from the group consisting of an amino-terminal fragment of full-length Notch terminating between the epidermal growth factor-like repeat domain and the transmembrane domain (in particular, between the Lin-12/Notch repeats and the transmembrane domain) of full-length Notch, and a carboxy-terminal fragment of full-length Notch with its amino terminus situated between the epidermal growth factor-like repeat domain and the transmembrane domain (in particular, between the Lin-12/Notch repeats and the transmembrane domain), or selected from the group consisting of Notch fragments having a molecular weight of about 270, 200, 170, 140, 110, 100, 90 and 85 kilodaltons. Yet another method is to detect a pattern of Notch cleavage products as shown in FIG. 10A or 10B.

Detection of such cleavage products can be done, e.g., by immunoprecipitating the cleavage products with an anti-Notch antibody or binding to anti-Notch antibody on an immunoaffinity column or immobilized on a plate or in a well, or visualizing the fragments by Western blotting. In a specific embodiment, the cleavage products can be labelled by general cell surface labeling, or, alternatively, by pulse labeling the cells by incubation in culture medium containing a radioactive label, or, alternatively, it can be anti-Notch antibody (or antibody binding partner) that is labeled rather than the Notch cleavage products.

According to a specific embodiment of the invention, antibodies and fragments containing the binding domain thereof, directed against Notch are used to detect. Notch in a specific embodiment of the above methods. Accordingly, Notch proteins, fragments or analogs or derivatives thereof, in particular, human Notch proteins or fragments thereof, may be used as immunogens to generate anti-Notch protein antibodies. Such antibodies can be polyclonal, monoclonal, chimeric, single chain, Fab fragments, or from an Fab expression library. In a specific embodiment, antibodies specific to EGF-like repeats 11 and 12 of Notch may be prepared. In other embodiments, antibodies reactive with the extracellular domain of Notch can be generated. In one embodiment, antibodies specific to human Notch are produced.

Various procedures known in the art may be used for the production of polyclonal antibodies to a Notch protein or peptide. In a particular embodiment, rabbit polyclonal antibodies to an epitope of the human Notch proteins depicted in FIGS. 2A-2D, or a subsequence thereof, can be obtained. For the production of antibody, various host animals can be immunized by injection with the native Notch protein, or a synthetic version, or fragment thereof, including but not limited to rabbits, mice, rats, etc. Various adjuvants may be used to increase the immunological response, depending on the host species, and including but not limited to Freund's (complete and incomplete), mineral gels such as aluminum hydroxide, surface active substances such as lysolecithin, pluronic polyols, polyanions, peptides, oil emulsions, keyhole limpet hemocyanins, dinitrophenol, and potentially useful human adjuvants such as BCG (bacille Calmette-Guerin) and corynebacterium parvum.

For preparation of monoclonal antibodies directed toward a Notch protein sequence, any technique which provides for the production of antibody molecules by continuous cell lines in culture may be used. For example, the hybridoma technique originally developed by Kohler and Milstein (1975, Nature 256:495-497), as well as the trioma technique, the human B-cell hybridoma technique (Kozbor et al., 1983, Immunology Today 4:72), and the EBV-hybridoma technique to produce human monoclonal antibodies (Cole et al., 1985, in Monoclonal Antibodies and Cancer Therapy, Alan R. Liss, Inc., pp. 77-96).

Antibody fragments which contain the idiotype (binding domain) of the molecule can be generated by known techniques. For example, such fragments include but are not limited to: the F(ab′)₂ fragment which can be produced by pepsin digestion of the antibody molecule; the Fab′ fragments which can be generated by reducing the disulfide bridges of the F(ab′)₂ fragment, and the Fab fragments which can be generated by treating the antibody molecule with papain and a reducing agent.

In the production of antibodies, screening for the desired antibody can be accomplished by techniques known in the art, e.g., ELISA (enzyme-linked immunosorbent assay). For example, to select antibodies which recognize the adhesive domain of a Notch protein, one may assay generated hybridomas for a product which binds to a protein fragment containing such domain. For selection of an antibody specific to human Notch, one can select on the basis of positive binding to human Notch and a lack of binding to Drosophila Notch.

Another method to detect the active form of Notch is to use a Notch ligand or other Notch binding partner or binding fragment thereof, such as Delta or Serrate and members of the Delta/Serrate family, to bind to Notch (e.g., when the ligand is labeled), or to recover Notch by coimmunoprecipitating with the appropriate anti-Notch ligand antibody to co-immunoprecipitate Notch cleavage products in the active Notch heterodimer bound to the Notch ligand, etc. Other Notch binding proteins, in addition to extracellular ligands, can also be used to co-immunoprecipitate Notch cleavage fragments. Examples of Notch ligands include but are not limited to Delta, Serrate, Deltex, and fragments and derivatives thereof that mediate binding to Notch; see e.g., International Publications WO 92/19734, WO 96/27610, WO 97/01571, and WO 97/18822.

Similar procedures to those described supra can be used to make antibodies to domains of other proteins (particularly toporythmic proteins) that bind or otherwise interact with Notch (e.g., binding fragments of Delta or Serrate).

Another method that can be used to detect the cell surface-expressed active form of Notch is to assay for cell adhesion between cells expressing Notch and cells expressing a Notch ligand, such as Delta or Serrate or members of the Delta/Serrate family, e.g., according to the method disclosed in Rebay et al., 1991, Cell 67:687-699 and International Publication WO 92/19734. In one aspect, this method comprises contacting a first plurality of said cell with a second plurality of cells expressing a Notch ligand on their surfaces; and measuring cell aggregation between cells in said first plurality and cells in second plurality.

The cell in which Notch activation is detected or measured can be any cell, e.g., one that endogenously or recombinantly expresses Notch. The cell can be vertebrate, insect (e.g., Drosophila), C. elegans, mammalian, bovine, murine, rat, avian, fish, primate, human, etc. The Notch which is expressed can be vertebrate, insect, C. elegans, mammalian, bovine, murine, rat, avian, fish, primate, human, etc. The cell can be a cell of primary tissue, a cell line, or of an animal containing and expressing a Notch transgene. For example, the transgenic animal can be a Drosophila (e.g., melanogaster) or a C. elegans. In a preferred embodiment, the transgene encodes a human Notch. Transgenic animals can be made by standard methods well known in the art (e.g., by use of P element transposons as a vector in Drosophila).

5.2 Methods of Identifying Modulators

In one embodiment of the invention, methods are provided for the identification of modulators, e.g., inhibitors, antagonists, or agonists, of Notch activation by detecting the ability of the modulators to effect cleavage of full length Notch and/or its expression on the cell surface. The invention is based, at least in part, on the discovery that the active form of Notch is not the full length protein but rather a cell surface-expressed heterodimer consisting of N^(EC) and N^(TM) Notch fragments (Notch cleavage products) tethered together through a reducing agent-sensitive linkage, in particular, a non-covalent, metal-ion-dependent (e.g., calcium ion-dependent) linkage. In one aspect of this embodiment of the invention, the method for identifying a modulator of Notch activation comprises providing a cell with a candidate modulator molecule and detecting or measuring the amount of Notch on the surface of the cell, in which a difference in the presence or amount compared to a cell not contacted with the candidate molecule indicates that the candidate molecule modulates Notch activation. In another aspect of this embodiment of the invention, the method comprises providing a cell with a candidate modulator molecule and detecting or measuring the expression by the cell of one or more Notch cleavage products selected from the group consisting of N^(EC) and N^(TM), in which a difference in the presence or amount of said one or more cleavage products compared to a Notch cell not contacted with the candidate molecule indicates that the molecule modulates Notch activity. In yet another aspect, the method comprises providing a cell with a candidate modulator molecule and detecting or measuring the amount of the expression by the cell of one or more fragments of Notch selected from the group consisting of an amino-terminal fragment of full-length Notch terminating between the epidermal growth factor-like repeat domain and the transmembrane domain (in particular, between the Lin-12/Notch repeats and the transmembrane domain) of full-length Notch, and a carboxy-terminal fragment of full-length Notch with its amino terminus situated between the epidermal growth factor-like repeat domain and the transmembrane domain (in particular, between the Lin-12/Notch repeats and the transmembrane domain); in which a difference in the presence or amount of said one or more fragments compared to a Notch cell not.contacted with the candidate molecule indicates that the molecule modulates Notch activity.

In yet another aspect, the method comprises providing a cell with a candidate modulator molecule and detecting or measuring the expression by the cell of one or more fragments of Notch selected from the group consisting of Notch fragments having a molecular weight of about 270, 200, 170, 140, 110, 100, 90 and 85 kilodaltons, in which a difference in the presence or amount of said one or more fragments compared to a Notch cell not contacted with the candidate molecule indicates that the molecule modulates Notch activity. In another aspect, the method comprises providing a cell with a candidate modulator molecule and detecting or measuring the amount of the expression by the cell of a pattern of Notch cleavage products as shown in FIG. 10A or 10B, in which a difference in the presence or amount of said pattern compared to a Notch cell not contacted with the candidate molecule indicates that the molecule modulates Notch activity. In yet another aspect, the method comprises providing a cell with a candidate modulator molecule and detecting or measuring the amount of the expression by the cell of one or more Notch fragments of about 180 kilodaltons and about 110 kilodaltons, respectively, in which a difference in the presence or amount of the fragments compared to a Notch cell not contacted with the candidate molecule indicates that the molecule modulates Notch activity. In another aspect, the method for identifying a modulator of Notch activation comprises contacting a cell with a candidate modulator molecule and detecting or measuring the amount of the expression by the cell of a Notch heterodimer containing a reducing agent-sensitive linkage, in a preferred aspect, a non-covalent, metal ion-dependent (e.g., calcium ion-dependent) linkage, in which a difference in the presence or amount of the heterodimer compared to a Notch cell not contacted with the candidate molecule indicates that the molecule modulates Notch activity. In a specific aspect of this embodiment of the invention, the detecting or measuring is carried out by contacting a first plurality of said cell with a second plurality of cells expressing a Notch ligand on their surfaces; and measuring cell aggregation between cells in said first plurality and cells in second plurality.

In yet another aspect of this embodiment of the invention, the method for identifying a modulator of Notch activation comprises contacting a candidate modulator molecule with a full length Notch in the presence of a composition comprising cellular proteins, under conditions conducive to cleavage of the full-length Notch by one or more components of the composition, and detecting or measuring the amount of Notch cleavage products N^(EC) and/or N^(TM) that result, in which a difference in the presence or amount of said Notch cleavage product(s) compared to a full-length Notch in presence of said composition not contacted with the candidate molecule indicates that the molecule modulates Notch activity. In another aspect, the method for identifying a modulator of Notch activation comprises contacting a candidate modulator molecule with a full length Notch in the presence of a composition comprising cellular proteins, under conditions conducive to cleavage of the full-length Notch by one or more components of the composition, and detecting or measuring one or more fragments of Notch selected from the group consisting of an amino-terminal fragment of full-length Notch terminating between the epidermal growth factor-like repeat domain and the transmembrane domain (in particular, between the Lin-12/Notch repeats and the transmembrane domain) of full-length Notch, and a carboxy-terminal fragment of full-length Notch with its amino terminus situated between the epidermal growth factor-like repeat domain and the transmembrane domain (in particular, between the Lin-12/Notch repeats and the transmembrane domain), that result, in which a difference in the presence or amount of said one or more Notch fragments compared to a full-length Notch in presence of said composition not contacted with the candidate molecule indicates that the molecule modulates Notch activity.

In yet another aspect, the method for identifying a modulator of Notch activation comprises contacting a candidate modulator molecule with a full length Notch in the presence of a composition comprising cellular proteins, under conditions conducive to cleavage of the full-length Notch by one or more components of the composition and detecting or measuring the amount of one or more fragments of Notch selected from the group consisting of Notch fragments having a molecular weight of about 270, 200, 170, 140, 110, 100, 90 and 85 kilodaltons, that result, in which a difference in the presence or amount of said one or more Notch fragments compared to a full-length Notch in presence of said composition not contacted with the candidate molecule indicates that the molecule modulates Notch activity. In yet another aspect, the method for identifying a modulator of Notch activation comprises contacting a candidate modulator molecule with a full length Notch in the presence of a composition comprising cellular proteins, under conditions conducive to cleavage of the full-length Notch by one or more components of the composition, and detecting or measuring the amount of a pattern of Notch cleavage products as shown in FIG. 10A or 10B that result, in which a difference in the presence or amount of said pattern compared to a full-length Notch in presence of said composition not contacted with the candidate molecule indicates that the molecule modulates Notch activity.

In yet another aspect of this embodiment of the invention, the method for identifying a modulator of Notch activation comprises contacting a candidate modulator molecule with a full length Notch in the presence of a composition comprising cellular proteins, under conditions conducive to cleavage of the full-length Notch by one or more components of the composition, and detecting or measuring the amount of one or more Notch fragments of about 180 kilodaltons and about 110 kilodaltons, respectively, that result, in which a difference in the presence or amount of said one or more Notch fragments compared to-a full-length Notch in presence of said composition not contacted with the candidate molecule indicates that the molecule modulates Notch activity. In yet another aspect, the method for identifying a modulator of Notch activation comprises contacting a candidate modulator molecule with a full length Notch in the presence of a composition comprising cellular proteins, under conditions conducive to cleavage of the full-length Notch by one or more components of the composition, and detecting or measuring the amount of a Notch heterodimer containing a reducing agent-sensitive linkage, in particular, a non-covalent, metal ion-dependent (e.g., calcium ion-dependent) linkage, that results, in which a difference in the presence or amount of said heterodimer compared to a full-length Notch in presence of said composition not contacted with the candidate molecule indicates that the molecule modulates Notch activity.

In a specific aspect of the embodiment using a composition comprising cellular proteins, the composition comprising cellular proteins is a cell lysate made from cells which recombinantly express Notch. In another specific aspect of this embodiment, the composition comprising cellular proteins is a cell lysate made from cells which endogenously express Notch.

Detection or measurement of Notch expressed on the cell surface and/or Notch cleavage products can be carried out by methods well known in the art and/or those methods. disclosed in Section 5.1, supra.

The cells used in the methods of this embodiment can either endogenously or recombinantly express Notch. Examples of the cell types and Notch protein that can be expressed are described in Section 5.1. Recombinant Notch expression is carried out by introducing Notch encoding nucleic acids into expression vectors and subsequently introducing the vectors into a cell to express Notch or simply introducing Notch encoding nucleic acids into a cell for expression. Nucleic acids encoding vertebrate and non-vertebrate Notch have been cloned and sequenced and their expression is well known in the art. See, for example, International Publication WO 92/19734 and U.S. Pat. No. 5,648,464, which are incorporated by reference in their entirety herein; Wharton et al., 1985, Cell 43:567-581; and Coffman et al., 1990, Science 249:1438-1441. Expression can be from expression vectors or intrachromosomal.

Any method known to those of skill in the art for the insertion of Notch-encoding DNA into a vector may be used to construct expression vectors containing a chimeric gene consisting of appropriate transcriptional/translational control signals and the protein coding sequences. These methods may include in vitro recombinant DNA and synthetic techniques and in vivo recombinants (genetic recombination). Expression of nucleic acid sequence encoding a Notch protein may be regulated by a second nucleic acid sequence so that the Notch protein is expressed in a host transformed with the recombinant DNA molecule. For example, expression of a Notch protein may be controlled by any promoter/enhancer element known in the art. Promoters which may be used to control Notch gene expression include, but are not limited to, the SV40 early promoter region (Bernoist and Chambon, 1981, Nature 290:304-310), the promoter contained in the 3′ long terminal repeat of Rous sarcoma virus (Yamamoto, et al., 1980, Cell:22 787-797), the herpes thymidine kinase promoter (Wagner et al., 1981, Proc. Natl. Acad. Sci. U.S.A. 78:1441-1445), the regulatory sequences of the metallothionein gene (Brinster et al., 1982, Nature 296:39-42); prokaryotic expression vectors such as the β-lactamase promoter (Villa-Kamaroff, et al., 1978, Proc. Natl. Acad. Sci. U.S.A. 75:3727-3731), or the tac promoter (DeBoer, et al., 1983, Proc. Natl. Acad. Sci. U.S.A. 80:21-25); see also “Useful proteins from recombinant bacteria” in Scientific American, 1980, 242:74-94; plant expression vectors comprising the nopaline synthetase promoter region (Herrera-Estrella et al., Nature 303:209-213) or the cauliflower mosaic virus 35S RNA promoter (Gardner, et al., 1981, Nucl. Acids Res. 9:2871), and the promoter of the photosynthetic enzyme ribulose biphosphate carboxylase (Herrera-Estrella et al., 1984, Nature 310:115-120); promoter elements from yeast or other fungi such as the Gal 4 promoter, the ADC (alcohol dehydrogenase) promoter, PGK (phosphoglycerol kinase) promoter, alkaline phosphatase promoter, and the following animal transcriptional control regions, which exhibit tissue specificity and have been utilized in transgenic animals: elastase I gene control region which is active in pancreatic acinar cells (Swift et al., 1984, Cell 38:639-646; Ornitz et al., 1986, Cold Spring Harbor Symp. Quant. Biol. 50:399-409; MacDonald, 1987, Hepatology 7:425-515); insulin gene control region which is active in pancreatic beta cells (Hanahan, 1985, Nature 315:115-122), immunoglobulin gene control region which is active in lymphoid cells (Grosschedl et al., 1984, Cell 38:647-658; Adames et al., 1985, Nature 318:533-538; Alexander et al., 1987, Mol. Cell. Biol. 7:1436-1444), mouse mammary tumor virus control region which is active in testicular, breast, lymphoid and mast cells (Leder et al., 1986, Cell 45:485-495), albumin gene control region which is active in liver (Pinkert et al., 1987, Genes and Devel. 1:268-276), alpha-fetoprotein gene control region which is active in liver (Krumlauf et al., 1985, Mol. Cell. Biol. 5:1639-1648; Hammer et al., 1987, Science 235:53-58; alpha 1-antitrypsin gene control region which is active in the liver (Kelsey et al., 1987, Genes and Devel. 1:161-171), beta-globin gene control region which is active in myeloid cells (Mogram et al., 1985, Nature 315:338-340; Kollias et al., 1986, Cell 46:89-94; myelin basic protein gene control region which is active in oligodendrocyte cells in the brain (Readhead et al., 1987, Cell 48:703-712); myosin light chain-2 gene control region which is active in skeletal muscle (Sani, 1985, Nature 314:283-286), and gonadotropic releasing hormone gene control region which is active in the hypothalamus (Mason et al., 1986, Science 234:1372-1378).

Many expression vectors can be used, including but not limited to, the following vectors or their derivatives: human or animal viruses such as vaccinia virus or adenovirus; insect viruses such as baculovirus; yeast vectors; bacteriophage vectors (e.g., lambda), and plasmid and cosmid DNA vectors, to name but a few.

In addition, a host cell strain may be chosen which modulates the expression of Notch, or modifies and processes the gene product in the specific fashion desired. Expression from certain promoters can be elevated in the presence of certain inducers; thus, expression of Notch protein may be controlled. Furthermore, different host cells have characteristic and specific mechanisms for the translational and post-translational processing and modification (e.g., glycosylation, cleavage) of proteins. Appropriate cell lines or host systems can be chosen to ensure the desired modification and processing of the Notch protein expressed. For example, expression in a bacterial system can be used to produce an unglycosylated core protein product. Expression in yeast will produce a glycosylated product. Expression in mammalian cells can be used to ensure “native” glycosylation of a mammalian Notch protein.

In the methods of the invention in which full-length Notch is incubated with compositions comprising cellular proteins (e.g., cell lysates or cell fractions) in the presence of candidate cleavage (and thus Notch activation) modulators the expression of Notch should be such that full length Notch is expressed and proteolytic cleavage of Notch is kept to a minimum such that Notch cleavage products are easily detected over any background proteolysis. There are several methods known in the art to keep proteolysis to a minimum. For example, one manner to keep Notch cleavage to a minimum is to express Notch in cells concurrently with Brefeldin A treatment. Brefeldin A has been shown to inhibit the cleavage of Notch, see Section 6.7, infra. Another manner to keep Notch cleavage to a minimum is to incubate Notch expressing cells at 19° C., see also Section 6.7, infra. Another manner is to express Notch in cells which do not contain a protease which cleaves Notch or to express Notch in an in vitro transcription-translation system in the presence of a protease inhibitor such as phenylmethylsulfonylfluoride (PMSF).

5.2.1 Candidate Molecules

Any molecule known in the art can be tested for its ability to modulate Notch activation as measured by the cell surface expression of Notch or the expression of one or more of the Notch cleavage products disclosed herein. For identifying a molecule that modulates Notch activation, candidate molecules can be directly provided to a cell expressing Notch, or, in the case of candidate proteins, can be provided by providing their encoding nucleic acids under conditions in which the nucleic acids are recombinantly expressed to produce the candidate proteins within the Notch expressing cell. In an embodiment of the invention directed to the assay using full-length Notch and a composition comprising cellular proteins, candidate molecules can also be added to a composition comprising cellular proteins (whole cell lysates, membrane fraction, etc.), preferably derived from cells endogenously or recombinantly expressing Notch.

This embodiment of the invention is well suited to screen chemical libraries for molecules which modulate, e.g., inhibit, antagonize, or agonize, Notch activation. The chemical libraries can be peptide libraries, peptidomimetic libraries, other non-peptide synthetic organic libraries, etc.

Exemplary libraries are commercially available from several sources (ArQule, Tripos/PanLabs, ChemDesign, Pharmacopoeia). In some cases, these chemical libraries are generated using combinatorial strategies that encode the identity of each member of the library on a substrate to which the member compound is attached, thus allowing direct and immediate identification of a molecule that is an effective modulator. Thus, in many combinatorial approaches, the position on a plate of a compound specifies that compound's composition. Also, in one example, a single plate position may have from 1-20 chemicals that can be screened by administration to a well containing the interactions of interest. Thus, if modulation is detected, smaller and smaller pools of interacting pairs can be assayed for the modulation activity. By such methods, many candidate molecules can be screened.

Many diversity libraries suitable for use are known in the art and can be used to provide compounds to be tested according to the present invention. Alternatively, libraries can be constructed using standard methods. Chemical (synthetic) libraries, recombinant expression libraries, or polysome-based libraries are exemplary types of libraries that can be used.

The libraries can be constrained or semirigid (having some degree of structural rigidity), or linear or nonconstrained. The library can be a cDNA or genomic expression library, random peptide expression library or a chemically synthesized random peptide library, or non-peptide library. Expression libraries are introduced into the cells in which the assay occurs, where the nucleic acids of the library are expressed to produce their encoded proteins.

In one embodiment, peptide libraries that can be used in the present invention may be libraries that are chemically synthesized in vitro. Examples of such libraries are given in Houghten et al., 1991, Nature 354:84-86, which describes mixtures of free hexapeptides in which the first and second residues in each peptide were individually and specifically defined; Lam et al., 1991, Nature 354:82-84, which describes a “one bead, one peptide” approach in which a solid phase split synthesis scheme produced a library of peptides in which each bead in the collection had immobilized thereon a single, random sequence of amino acid residues; Medynski, 1994, Bio/Technology 12:709-710, which describes split synthesis and T-bag synthesis methods; and Gallop et al., 1994, J. Medicinal Chemistry 37(9):1233-1251. Simply by way of other examples, a combinatorial library may be prepared for use, according to the methods of Ohlmeyer et al., 1993, Proc. Natl. Acad. Sci. USA 90:10922-10926; Erb et 15 al., 1994, Proc. Natl. Acad. Sci. USA 91:11422-11426; Houghten et al., 1992, Biotechniques 13:412; Jayawickreme et al., 1994, Proc. Natl. Acad. Sci. USA 91:1614-1618; or Salmon et al., 1993, Proc. Natl. Acad. Sci. USA 90:11708-11712. PCT Publication No. WO 93/20242 and Brenner and Lerner, 1992, Proc. Natl. Acad. Sci. USA 89:5381-5383 describe “encoded combinatorial chemical libraries,” that contain oligonucleotide identifiers for each chemical polymer library member.

Further, more general, structurally constrained, organic diversity (e.g., nonpeptide) libraries, can also be used. By way of example, a benzodiazepine library (see e.g., Bunin et al., 1994, Proc. Natl. Acad. Sci. USA 91:4708-4712) may be used.

Conformationally constrained libraries that can be used include but are not limited to those containing invariant cysteine residues which, in an oxidizing environment, cross-link by disulfide bonds to form cystines, modified peptides (e.g., incorporating fluorine, metals, isotopic labels, are phosphorylated, etc.), peptides containing one or more non-naturally occurring amino acids, non-peptide structures, and peptides containing a significant fraction of γ-carboxyglutamic acid.

Libraries of non-peptides, e.g., peptide derivatives (for example, that contain one or more non-naturally occurring amino acids) can.also be used. One example of these are peptoid libraries (Simon et al., 1992, Proc. Natl. Acad. Sci. USA 89:9367-9371). Peptoids are polymers of non-natural amino acids that have naturally occurring side chains attached not to the alpha carbon but to the backbone amino nitrogen. Since peptoids are not easily degraded by human digestive enzymes, they are advantageously more easily adaptable to drug use. Another example of a library that can be used, in which the amide functionalities in peptides have been permethylated to generate a chemically transformed combinatorial library, is described by Ostresh et al., 1994, Proc. Natl. Acad. Sci. USA 91:11138-11142).

The members of the peptide libraries that can be screened according to the invention are not limited to containing the 20 naturally occurring amino acids. In particular, chemically synthesized libraries and polysome based libraries allow the use of amino acids in addition to the 20 naturally occurring amino acids (by their inclusion in the precursor pool of amino acids used in library production). In specific embodiments, the library members contain one or more non-natural or non-classical amino acids or cyclic peptides. Non-classical amino acids include but are not limited to the D-isomers of the common amino acids, α-amino isobutyric acid, 4-aminobutyric acid, Abu, 2-amino butyric acid; γ-Abu, ε-Ahx, 6-amino hexanoic acid; Aib, 2-amino isobutyric acid; 3-amino propionic acid; ornithine; norleucine; norvaline, hydroxyproline, sarcosine, citrulline, cysteic acid, t-butylglycine, t-butylalanine, phenylglycine, cyclohexylalanine, β-alanine, designer amino acids such as β-methyl amino acids, Cα-methyl amino acids, Nα-methyl amino acids, fluoro-amino acids and amino acid analogs in general. Furthermore, the amino acid can be D: (dextrorotary) or L (levorotary).

Further, toporythmic proteins, derivatives and fragments thereof, can be tested for the ability to modulate Notch activation. Toporythmic proteins, and more generally, members of the “Notch cascade” or the “Notch group” of genes, include Notch, Delta, Serrate, and other members of the Delta/Serrate family, which are identified by genetic (as detected phenotypically, e.g., in Drosophila) or molecular interaction (e.g., binding in vitro). See, International Publications WO 92/19734, WO 97/18822, WO 96/27610, and WO 97/01571 and references therein, for examples of vertebrate and non-vertebrate members of the Notch family of genes.

5.3 Heterodimeric Notch

The present invention is also directed to a substantially purified heterodimeric form of Notch comprising Notch fragments tethered together through a reducing agent-sensitive linkage, in particular, a non-covalent, metal ion-dependent (e.g., calcium ion-dependent) linkage. In its active state Notch is a heterodimer of an about (±10%) 180 kilodaltons (kDa) subunit (N^(EC)) and an about (±10%) 110 kDa subunit (N^(TM)), which are tethered together through a reducing agent-sensitive linkage, particularly, a non-covalent, metal ion-dependent (e.g., calcium ion-dependent) linkage. As shown by way of example infra, the two subunits arise due to a proteolytic cleavage of the full length Notch molecule in the trans-Golgi at a site in Notch amino-terminal to the transmembrane domain and carboxy-terminal to the EGF repeat region, thus generating an extracellular fragment (N^(EC)) of about 180 kDa and a transmembrane/intracellular fragment (N^(TM)) of about 110 kDa.

The present invention is also directed to an amino-terminal fragment of full-length Notch terminating between the epidermal growth factor-like repeat domain and the transmembrane domain (in particular, between the Lin-12/Notch repeats and the transmembrane domain) of full-length Notch. The present invention is also directed to a carboxy-terminal fragment of full-length Notch with its amino terminus situated between the epidermal growth factor-like repeat domain and the transmembrane domain (in particular, between the Lin-12/Notch repeats and the transmembrane domain).

Nucleic acids encoding vertebrate and non-vertebrate Notch have been cloned and sequenced. See, for example, WO 92/19734 and U.S. Pat. No. 5,648,464, which are incorporated by reference in their entirety herein; Wharton et al., 1985, Cell 43:567-581; and Coffman et al., 1990, Science 249:1438-1441. These nucleic acids can be used to express the full length Notch molecule either in vivo or in vitro, and either the full length molecule is isolated and then proteolytically cleaved (e.g., by exposure to cell lysates) or the full-length Notch is physiologically cleaved by the cell and the fragment(s) are then isolated therefrom. Also, the Notch encoding nucleic acids can be subcloned to express the two subunits N^(EC) and N^(TM), respectively, either in vivo or in vitro, which can then be isolated, and if desired, can then be tethered together by addition of, or in the presence of, Ca²⁺ to form a non-covalent, metal ion-dependent, reducing agent-sensitive linkage.

The present invention is also directed to pharmaceutical compositions comprising the heterodimeric form of Notch, or the amino-terminal fragment, or the carboxy-terminal fragment, or mixtures thereof suitable for in vivo administration, in combination with a pharmaceutically acceptable carrier or excipient. Such a carrier includes but is not limited to saline, buffered saline, dextrose, water, glycerol, ethanol, and combinations thereof. The carrier and composition can be sterile. The formulation should suit the mode of administration.

The composition, if desired, can also contain minor amounts of wetting or emulsifying agents, or pH buffering agents. The composition can be a liquid solution, suspension, emulsion, tablet, pill, capsule, sustained release formulation, or powder. The composition can be formulated as a suppository, with traditional binders and carriers such as triglycerides. Oral formulation can include standard carriers such as pharmaceutical grades of mannitol, lactose, starch, magnesium stearate, sodium saccharine, cellulose, magnesium carbonate, etc.

In a preferred embodiment, the composition is formulated in accordance with routine procedures as a pharmaceutical composition adapted for intravenous administration to human beings. Typically, compositions for intravenous administration are solutions in sterile isotonic aqueous buffer. Where necessary, the composition may also include a solubilizing agent and a local anesthetic such as lignocaine to ease pain at the site of the injection. Generally, the ingredients are supplied either separately or mixed together in unit dosage form, for example, as a dry lyophilized powder or water free concentrate in a hermetically sealed container such as an ampoule or sachette indicating the quantity of active agent. Where the composition is to be administered by infusion, it can be dispensed with an infusion bottle containing sterile pharmaceutical grade water or saline. Where the composition is administered by injection, an ampoule of sterile water for injection or saline can be provided so that the ingredients may be mixed prior to administration.

The invention also provides a pharmaceutical pack or kit comprising one or more containers filled with one or more of the ingredients of the pharmaceutical compositions of the invention. Optionally associated with such container(s) can be a notice in the form prescribed by a governmental agency regulating the manufacture, use or sale of pharmaceuticals or biological products, which notice reflects approval by the agency of manufacture, use or sale for human administration.

6. Intracellular Cleavage of Notch Leads to a Heterodimeric Receptor on the Plasma Membrane

Previous models for signal transduction via the Notch pathway have depicted the full-length Notch receptor expressed at the cell surface. Evidence is presented herein demonstrating that the Notch receptor on the plasma membrane is cleaved. This cleavage is an evolutionary conserved, general property of Notch and occurs in the trans-Golgi network as the receptor traffics towards the plasma membrane. although full-length Notch is detectable in the cell, it does not reach the surface. Cleavage results in a C-terminal fragment, N^(TM), which appears to be cleaved N-terminal to the transmembrane domain, and an N-terminal fragment N^(EC) that contains most of the extracellular region. Evidence is provided herein that these fragments are tethered together on the plasma membrane by a link that is sensitive to reducing conditions and dependent upon the presence of metal ions, forming a heterodimeric receptor. On the basis of the experimental evidence gathered, it is proposed that the active, ligand accessible form of the receptor is the heterodimeric form, whereas full-length Notch reflects newly synthesized, intracellular and, hence, inactive molecules.

6.1 Materials and Methods

6.1.1 Isolating and Sequencing Human Notch2 cDNAs

A human fetal brain cDNA Zap II library (from 17-18 week embryo; Stratagene, La Jolla, Calif.) was used in the screening for human Notch homologs. The Notch cDNA clones were originally obtained by using a probe encoding portions of the human Notch2 protein (hN2K and hN5K), (Stifani et al., 1992, Nature Genetics 2:119-127). A probe used to screen for cDNAs spanning 5′ regions of the human Notch2 gene was generated from the hN2K cDNA. Because the extreme 5′ terminus of the human Notch2 gene was not isolated using this probe, advantage was taken of the fortuitous isolation of a human Notch2 cDNA (Adams, et al., 1993, Nature Genetics 4:256-267) that extends further 5′, as determined by sequence comparison to the rat Notch2 cDNA isolated by Weinmaster et al., 1992, Development 116:931-941. Although this human cDNA does not extend to the extreme 5′ end of the human Notch2 coding region, it was used to generate a new probe that was closer to the 5′ end of the gene. This probe was used to isolate the 5′-most cDNAs encoding human Notch2. Sequencing was done using the Sequenase™ Kit (United States Biochemical Corporation, Cleveland, Ohio).

6.1.2 Cell Culture

Human neuroblastoma (SJ-NB5) cells were grown at 37° C. in an atmosphere of 5% CO₂/95% air, in RPMI (Gibco-BRL, Grand Island, N.Y.) supplemented with 10% fetal bovine serum (Gibco BRL, Grand Island, N.Y.), 2 mM L-Glutamine (ICN Biomedicals, Inc., Costa Mesa, Calif.), 100 μg/ml penicillin, and 100 μg/ml streptomycin (ICN Biomedicals, Inc., Costa Mesa, Calif.). Cells were dissociated using phosphate buffered saline (PBS) with 0.25% trypsin and 0.03% EDTA (J. T. Baker, Inc., Phillipsburg, N.J.), and subcultured at ratios of 1:3 to 1:10. HaCat Cells (cultured human keratinocytes) were a gift from Dr. Michael Reiss (Yale University). Aggregation experiments and the maintenance of Drosophila S2 and KC cells were as described in Fehon et al., 1990, Cell 61:523-534.

6.1.3 Antibodies

Antibodies bhN6D and bTAN20 are monoclonal antibodies (rat, IgG) directed against the non-conserved intracellular epitopes of human Notch2 and Notch1, respectively (Zagouras et al., 1995, Proc. Natl. Acad. Sci. USA 92:6414-6418). On western blots they recognize specifically Notch1 and Notch2 but are not useful for immunoprecipitations. In contrast, antibody PGHN, a polyclonal antibody (Rabbit, IgG) directed against intracellular epitopes of human Notch2, can be used to immunoprecipitate Notch2 (Zagouras et al., 1995, Proc. Natl. Acad. Sci. USA 92:6414-6418). The Drosophila antibody 9C6 is a monoclonal antibody which recognizes intracellular epitopes of Notch (Fehon et al., 1990, Cell 61:523-534).

6.1.4 Subcellular Fractionation and Western Blotting

SJ-NB5 cells were grown to 80-90% confluence in six T-75 tissue culture flasks, scraped in TBS, washed once and resuspended in 1 ml cold buffer A (75 mM KCl; 10 mM imidazole, pH 7.2; 1 mM EGTA; 2.5 MM MgCl₂; 0.02% NaN₃; 1 mM DTT; and 1 mM Pefabloc SC [Boehringer Mannheim]). During the fractionation process all samples were kept on ice and resuspended in cold buffer A. Pellet samples at all stages of fractionation were resuspended in their original volumes so that stoichiometric ratios of all samples would be equivalent.

Cells were homogenized using Omini's hand homogenizer with microscopic monitoring of cell lysis throughout homogenization. A 50 μl aliquot was kept as Fraction 1 (whole cell lysate). The lysate was then centrifuged at low speed (900×g) for 5 minutes at 4° C. The resulting pellet was resuspended in buffer A, with a 50 μl aliquot of the suspension as Fraction 2 (0.9K/P). The suspension was centrifuged again. The pellet was washed once with buffer A. After a third centrifugation, the pellet was resuspended in 200 μl buffer A, mixed with 1.8 ml 60% sucrose made in buffer A containing 5 mM MgCl₂, and then transferred to a Beckman SW 50.1 centrifuge tube. The suspension was overlaid with 2 ml 40% sucrose-buffer A, and then 2 ml buffer A. The sample was centrifuged at 100,000×g for 1 hr at 4° C. Two banded fractions were collected separately and 50 μl aliquots were kept. The upper and lower fractions were termed 40/0 and 40/50, respectively, and the nuclear pellet at bottom was resuspended in buffer A and designated NP.

The supernatant from the 900×g spin was centrifuged again at 40,000×g for 15 minutes at 4° C. using a Sorval SS-34 fixed angle rotor. The pellet from this mid-speed spin was resuspended in buffer A and designated 40K/P. The supernatant from the mid-speed spin was further centrifuged at 100,000×g for 1 hr at 4° C. using a Beckman 70 Ti fixed angle rotor. The pellet was again resuspended in buffer A and termed 100K/P. The supernatant was labeled 100K/S.

All samples were resuspended in 10× sample buffer, boiled and subjected to 4-20% SDS-PAGE, transferred to nitrocellulose and western blotted as described in Stifani et al., 1992, Nature Genetics 2:119-127. For western blotting, a culture supernatant of anti-human Notch2 antibody bhN6D, which recognizes the intracellular domain of human Notch2, was used at a dilution of 1:10.

6.1.5 Biotinylation

Cells were grown in 10 cm plastic tissue culture plates to ˜80% confluence. Six plates were used per sample (+ or −biotin). Cells were washed four times with cold PBS/CMG (PBS/0.1 mM CaCl₂/1.0 MM MgCl₂/1.0 % glucose/pH˜8.0). 1.7 ml of fresh, cold PBS/CMG+/−Sulfo-NHS-biotin was added to each plate, then incubated at 4° C. for 15 minutes with shaking. This solution was replaced with cold RPMI without serum to absorb excess biotin, and cells were pipetted off the plates in cold serum free RPMI medium and incubated at 4° C. for 15 minutes. The cells were washed three times in cold PBS/CMG solution, and were then lysed in 1.2 ml lysis buffer per sample as described in Zagouras et al., 1995, Proc. Natl. Acad. Sci. USA 92:6414-6418. After addition of SDS to 0.2%, the samples were divided into three equal portions (˜400 μl each) for precipitation: 20 μl immobilized streptavidin (Immunopure Immobilized Streptavidin, Pierce, Rockford, Ill.); 2 μl anti-human Notch2 antibody PGHN (as described in Zagouras et al., 1995, Proc. Natl. Acad. Sci. USA 92:6414-6418), or 2 μl normal rabbit serum (NRbS) as a negative control. Samples were incubated overnight at 4° C. Staphylococcus aureus (Sigma Chemical Co., St. Louis, Mo.) was added to PGHN and NRbS samples at 80 μl per sample and incubations continued at 4° C. for 30 minutes. All samples were washed two times in 500 μl RIPA buffer A (10 mM Tris-HCl, pH 7.4/1% Triton X-100/0.1% SDS/1% Sodium Deoxycholate/150 mM NaCl) with 2.5 ug/ml antipain (Sigma Chemical Co., St. Louis, Mo.), 2.5 μg/ml aprotinin (Sigma Chemical Co., St. Louis, Mo.), 2 μM leupeptin (Sigma Chemical Co., St. Louis, Mo.), 2.5 μg/ml pepstatin (Sigma Chemical Co., St. Louis, Mo.), and 1 mM mg/ml phenylmethylsulfonyl fluoride (Sigma Chemical Co., St. Louis, Mo.). Samples were resuspended in 2×sample buffer, boiled, and subjected to SDS-polyacrylamide gel electrophoresis.

6.1.6 Pulse Chase and Brefeldin A Treatment

SJ-NB5 cells were grown on 60 mm petri dishes until ˜80% confluent, washed once with PBS, and then incubated in methionine and cysteine free DMEM medium for 1 hr. 100 μCi ³⁵S-translabled Met-Cys (ICN) was added to each plate, pulsed at 37° C. for 20 minutes, and chased for varying times and temperatures. The chase began by adding 2× volume complete medium plus 100 μg/ml cold methionine and cysteine to the plates.

For Brefeldin A samples, Brefeldin A was maintained at a final concentration of 10 μg/ml in starvation medium as well as in both pulse and chase. Cells were washed with cold PBS and lysed in lysis buffer (Zagouras et al., 1995, Proc. Natl. Acad. Sci. USA 92:6414-6418) containing 1 mM Pefabloc SC, 0.7 μg/ml pepstatin A, and 0.5 μg/ml leupeptin. Cell lysates were centrifuged at 14,000 rpm for 5 minutes. The supernatants were transferred to fresh tubes and pre-cleared by incubating with 5 μl normal rabbit serum and 50 μl 10% protein A-sephrose CL-4B (Pharmacia LKB) for 1 hr at 4° C. The beads were pelleted by centrifugation and the supernatants were divided into two equal aliquots. One aliquot was immunoprecipitated by incubating with rabbit polyclonal anti-human Notch2 antibody PGHN and 50 μl protein A-sephrose CL-4B for 2-3 hrs or overnight at 4° C. The other aliquot was immunoprecipitated by normal rabbit serum as control. The beads were washed three times in RIPA buffer B (150 mM NaCl, 1% NP40, 0.5% DOC, 0.1% SDS, 50 mM Tris, pH 7.5); washed once in 50 mM Tris-Cl, 150 mM NaCl, pH 7.5; resuspended in 50 μl SDS-sample buffer; boiled; and subjected to a 3-15% gradient SDS-PAGE gel. The gel was fixed in 25% iso-propanol, 10% acetic acid for 30 minutes, soaked in Amplify™ (Amersham) for 15-30 minutes, dried, and exposed to X-ray film at −70° C.

6.1.7 Pulse Chase and Biotinylation

SJ-NB5 cells were grown on 100 mm petri dishes until ˜80% confluent and pulse chased as described in Section 6.1.6 above. The pulse-chase times shown are described in the description of the figures. After pulse-chase, the plates were put on ice, washed three times in cold PBS (containing 0.1 mM CaCl₂, 1 mM MgCl₂), and then incubated 30 minutes at 4° C. in 2 ml biotinylation buffer (10 mM triethanolamine, pH 9.0, 2 mM CaCl₂, and 150 mM NaCl) containing 1 mg/ml NHS-SS-Biotin (Pierce, Rockford, Ill.) (freshly diluted from a 200 mg/ml DMSO stock stored at −20° C.) with very gentle shaking, and subsequently incubated in PBS-CMG buffer (0.1 mMCaCl₂, 1 mM MgCl₂, 100 mM Glycine) for another 30 minutes to quench unreacted biotin. Post incubation plates were washed twice in PBS-CM buffer to wash away the quenched biotin. Finally, the cells were lysed and immunoprecipitated by PGHN as previously described. After the final wash, the beads were divided equally into two aliquots. One aliquot was boiled in SDS-sample buffer, the second aliquot was incubated in 100 μl elution buffer (1% SDS, 50 mM Tris-Cl, 150 mM NaCl, pH 7.5) at 80° C. for 10 minutes, then 900 μl of lysis buffer was added to the eluted protein. After centrifugation, the supernatant was transferred to a fresh tube containing 50 μl of packed streptavidin beads (Pierce, Rockford, Ill.), and incubated at 4° C. for 2-3 hrs. The beads were washed and boiled in SDS-sample buffer as described above. The samples were analyzed by 3-15% SDS-PAGE electrophoresis. The gel was fixed in 25% iso-propanol, 10% acetic acid for 30 minutes, soaked in Amplify (Amersham) for 15-30 minutes, dried, and exposed to X-ray film at −70° C.

6.2 Characterization of the Human Notch2 Gene

The full-length cDNA encoding the human Notch2 protein is 7.8 kb in length, and the predicted protein product is 2471 amino acids long. This protein has all of the expected domains of Notch family proteins and is 92% identical to the rat Notch2 amino acid sequence overall. An amino acid alignment of human Notch2 (SEQ ID NO:1) with human Notch1 (SEQ ID NO:2), Xenopus Notch (Xotch) (SEQ ID NO:3) and Drosophila Notch (SEQ ID NO:4) is shown in FIGS. 2A-2D.

36 EGF repeats are present in all of the proteins shown, and each is more closely related to the corresponding EGF repeat in the other Notch homologs than to neighboring EGF repeats within the same protein. The overall identity for the EGF repeat region between the human Notch paralogs is 59%, while the identity levels between the Drosophila and human proteins in this region are slightly lower (51% for human Notch1 and 52% for human Notch2). While the overall amino acid conservation across the EGF repeat domain is low, the conservation of individual EGF repeats from one protein to another is variable (M. Baron and S. Artavanis-Tsakonas, unpublished results). Certain repeats, including numbers 11 and 12, which are capable of ligand-binding (Rebay et al., 1991, Cell 67:687-699), are more highly conserved than others. The overall conservation of the LN repeats is similar to that for the EGF repeats, having 54% identity between the human homologs and slightly lower values between Drosophila Notch and either human Notch1 or human Notch2 (49% and 44%, respectively).

In Notch2, the conservation of the intracellular domain is high. All of the known structural hallmarks of the Notch proteins are maintained, including the Ankyrin repeats, the PEST-containing region, and the basic stretch of amino acids which can function-as nuclear localization signals and target truncated forms of the protein into the nucleus (Stifani et al., 1992, Nature Genetics 2:119-127; Lieber et al., 1993, Genes and Development 7:1949-1965).

6.3 The Notch2 Protein Is Cleaved

Antibodies raised specifically against the human Notch2 protein were used to study its expression in cultured cells (Antibody bhN6D). Western blotting of Notch2 protein from the human SJ-NB5 neuroblastoma cell line revealed the presence of an approximately 110 kD (N^(TM)) polypeptide in addition to the full-length 300 kD protein (FIG. 3A, lane 1). This lower molecular weight polypeptide is the predominant species recognized by the antibody used in this experiment. A similar processing pattern is seen in HaCat cells (FIG. 3A, lane 2), a human keratinocyte cell line. The observed processing pattern is not confined to cell lines. The predominant polypeptide species recognized by the same antibody in rat embryo extracts and in a variety of human tissue extracts is also the 110 kD Notch breakdown product (FIG. 3A, lane 3, and FIG. 3B). Note that this western blot analysis reveals differences in the relative ratio of the full-length protein and the N^(TM) derivative among the examined tissues.

6.4 Cleavage Is a General Property of the Notch Receptor

Whether the characteristic cleavage pattern of the human Notch2 paralog is peculiar only to this molecule or whether it reflects a general pattern for the Notch receptor family was examined. Western blot analysis, using an antibody raised against the human Notch1 paralog (antibody bTAN20), demonstrates that this protein displays a processing pattern that is similar to that of Notch2 (FIG. 3C and FIG. 3D). These results are compatible with earlier analyses involving Notch1. The existence of a prominent approximately 120 kD fragment was previously demonstrated in extracts of two different human cell lines that express the Notch1 paralog (Aster et al., 1994, Cold Spring Harbor Symposia on Quantitative Biology 59:125-136). When a Notch1 expression plasmid is transfected into a baby hamster kidney cell line (BHK cells), the major Notch peptide detected in these cells by western blot analysis is a 110 kD species (data not shown, and Zagouras et al., 1995, Proc. Natl. Acad. Sci. USA 92:6414-6418).

In order to determine whether the processing pattern seen for Notch1 and Notch2 is specific to mammalian Notch proteins, western blotting of Drosophila cell lysates was performed, using an antibody raised against intracellular epitopes of Drosophila Notch (FIG. 3E; Fehon et al., 1990, Cell 61:523-534). In an embryonic extract, in addition to the clearly detectable full-length protein, several smaller Notch polypeptides, including an approximately N band, are visible. In the KC cell line, which expresses Notch endogenously, N^(TM) is clearly detectable. Finally, in an S2 cell line, which does not express endogenous Notch but has been stably transfected with a Notch expression plasmid, N^(TM) is also prominent. It is concluded that the processing of the Notch receptor is a general property of the Notch proteins.

6.5 N^(TM) Is Associated with Membranes

The subcellular localization of the Notch polypeptides was determined by cell fractionation. SJ-NB5 cells were fractionated as described in Section 6.1 and the resulting fractions were examined by western blotting. FIG. 4 shows a fractionation experiment in which the N^(TM) Notch fragment is associated with membrane lanes. Each fraction was also tested for the presence of syntaxin, a plasma membrane protein expressed in the same cell line (Bennett et al., 1992, Science 257:255-259). In order to ensure that such fractionation pattern is not confined to the SJ-NB5 cell line, HaCat cells and Drosophila S2 cells that were stably transfected with a Notch expression plasmid were fractionated (data not shown) and similar results were obtained.

6.6 The Notch Receptor Presented at the Cell Surface Is Cleaved

The association of the N^(TM) Notch fragment with the plasma membrane was further examined by biotin labeling of live SJ-NB5 cells (FIG. 5). Biotin labeling of surface proteins was performed by incubating live cells on ice in medium containing biotin (control cells were treated with the same medium lacking biotin). The cells were subsequently lysed and divided into three equal portions that were incubated with the following reagents: (1) immobilized streptavidin, which precipitates only biotin-labeled proteins, (2) the anti-Notch2 antibody PGHN, a polyclonal antibody which recognizes an intracellular epitope and immunoprecipitates human Notch2 (Zagouras et al., 1995, Proc. Natl. Acad. Sci. USA 92:6414-6418), and (3) normal rabbit serum (NRbS). Western blotting of the precipitated products was performed using the anti-Notch2 antibody, bhN6D. The results of this experiment are shown in FIG. 5. The only Notch2-related surface protein that was detected is the N^(TM) breakdown product. Immobilized streptavidin precipitated only the N^(TM) product in the biotin-labeled samples (lane 1) and no protein in the unlabeled samples (lane 4). In contrast, anti-Notch2 antibody PGHN efficiently precipitated both the full-length and breakdown Notch2 products in biotinylated (lane 2) and non-biotinylated samples (lane 5).

As expected, the negative control, NRbS, does not precipitate either protein form (lanes 3 and 6).

Based on the above results it is concluded that the N^(TM) fragment is a transmembrane Notch polypeptide that resides on the plasma membrane and must be the result of a cleavage at a site in the extracellular domain.

6.7 Notch Is Cleaved in the Trans-Golgi Network Before Reaching the Surface

The experiments described above demonstrate that the steady state form of the Notch receptor found at the cell surface is a cleaved form. In an attempt to determine the cellular compartment where Notch is cleaved, pulse labeling analyses were carried out in the presence of drugs that are known to interfere with cellular trafficking. FIG. 6A demonstrates that Brefeldin A, which blocks transport between the cis- and trans-Golgi network, effectively blocks the breakdown of full-length Notch. In contrast, monensin or chloraquinone do not affect processing (data not shown). Cleavage is also effectively blocked at 19° C., a characteristic feature of processing events that occur in the trans-Golgi network (FIG. 6B).

6.8 The Cleaved Extracellular Domain of Notch Is Tethered to the N^(TM) Transmembrane Fragment

In the aforementioned pulse labeling experiments (FIGS. 6A-6B), the accumulation of the N^(TM) fragment is closely paralleled by the accumulation of a larger fragment that is approximately 180 kD in molecular weight. This larger fragment is co-immunoprecipitated by the antibody PGHN, which recognizes an intracellular epitope of human Notch2. However, blotting of the same immunoprecipitate by western blot, using antibody bhN6D, also raised against an intracellular epitope, detects only the N^(TM) fragment.

A single cleavage of the Notch protein that produces a 110 kD fragment would also generate a second fragment of approximately 180 kD. It was therefore presumed that the N^(EC) fragment, which accumulates with kinetics indistinguishable from those of N^(TM), corresponds to the cleaved extracellular domain of the Notch2 protein that remains attached to the N^(TM) polypeptide by a SDS and/or DTT sensitive linkage. Antibodies recognizing extracellular epitopes were not possessed by us for western blot analysis. However, the relatedness of these fragments is also supported by the fact that the appearance of N^(EC) is not inhibited by monensin or chloraquinone (data not shown) but is inhibited by Brefeldin A and a 19° C. block (FIG. 6A). Additional supporting evidence comes from pulse labeling experiments done with a cysteine rather than a methionine label. Labeling with cysteine shows that the N^(EC) band incorporates nearly an order of magnitude more label than the N^(TM) band, consistent with the hypothesis that it carries most of the Notch extracellular domain (data not shown).

Additional biochemical data shows that the tethering of N^(EC) to N^(TM) is not only reducing agent-sensitive but is also metal ion-dependent. FIG. 11A is a Western blot analysis demonstrating that N^(EC) is present in the supernatant of Notch expressing S2 cells that have been resuspended in 2 mM EDTA, Tris-HCl saline buffer (EDTA), whereas in the presence of 2 mM CaCl₂ (Ca²⁺) insignificant amounts of N^(EC) are detected. Briefly, Drosophila S2 cells were induced to express Notch with the addition of 0.7 mM CuSO₄ for 16 hours; Notch expression was under the control of the metallothionien promoter (Fehon et al., 1990, Cell 61:523-534). The cells were washed once with 20 mM Tris-HCl, 150 mM NaCl, 2 mM CaCl₂ (TBS/Ca²⁺) and were resuspended in TBS/Ca²⁺ or in 20 mM Tris-HCl, 150 mM NaCl, 2 mM EDTA (TBS/EDTA) and incubated for one hour at room temperature under slow rocking. The cells were centrifuged and pelleted and the supernatants were collected for SDS-PAGE and Western blot analysis. The blot was probed with a monoclonal antibody directed to the extracellular domain of Notch, specifically against EGF-like repeats 5-7 of Drosophila Notch (clone C461.3B). This monoclonal was detected using goat anti-mouse horseradish peroxidase secondary antibody and chemiluminescent substrate.

FIG. 11B is a Western blot of a sucrose density centrifugation of S2 cell extracts that shows N^(EC) and N^(TM) co-sediment in the presence of CaCl₂, whereas N^(EC) and N^(TM) sediment separately in the presence of EDTA. Briefly, S2 expressing Notch cell extracts were prepared in either TBS/Ca²⁺ or TBS/EDTA with 1% Triton X-100, a non-ionic detergent, 1 mM PMSF, Pepstatin and Aprotinin each at 2 μg/mL and 1.8 μM Leupeptin. The extracts were sedimented through a 5-20% sucrose gradient in the above-respective buffers (without the protease inhibitors) in a Beckman SW50.1 rotor at 34,000 rpm for 16 hours at 4° C. Fractions were collected and precipitated with 10% trichloroacetic acid. The protein pellets were resuspended in SDS-PAGE sample buffer and analyzed by SDS-PAGE and Western blotting. Blots were probed with a mixture of monoclonal antibodies C461.3B and 9C6 (directed against the intracellular domain of Notch) and detected as described above.

These data demonstrate that N^(EC) and N^(TM) dissociate in the presence of calcium ion chelators such as EDTA and EGTA. Other evidence (not shown) shows that dissociated N^(EC) and N^(TM) can reassociate upon addition of calcium. Moreover, the interaction is sensitive to reducing agents such as β-mercaptoethanol and dithiothreitol (DTT), which are likely to act by disrupting the intra-chain disulfide bonds necessary to provide the secondary structure necessary for the Notch inter-chain interactions.

These data demonstrate that N^(EC) and N^(TM) are tethered through a non-covalent, metal ion-dependent, reducing agent-sensitive linkage, not through a disulfide bridge. Although the interaction between N^(EC) and N^(TM) does not appear to be dependent on inter-chain disulfide bond(s), intra-chain disulfide bond(s) appear to play a role in maintaining secondary structure such that N^(EC) and N^(TM) are able to interact.

6.9 Full Length Notch does not Reach the Cell Surface

The western blot analyses revealing the existence of the N^(TM) Notch fragment (FIG. 3) also show varying amounts of full-length Notch. Therefore, the fate of the full-length molecule was explored by testing its expression at the cell surface.

SJ-NB5 cells were labeled with [³⁵S]-methionine for 10 minutes and then chased for varying periods. The live cells were incubated with Biotin as described above, subsequently lysed, and immunoprecipitated with PGHN. The immunoprecipitate was divided into two equal portions, one of which was re-precipitated with immobilized streptavidin. The two sets of samples were then examined by SDS gel electrophoreses followed by fluorography. FIG. 7 shows that negligible amounts of full-length Notch are detected on the surface throughout the chase, while substantial amounts of full-length molecules are precipitated by the Notch antibody (total cellular Notch). As the full-length, newly synthesized Notch decreases during the chase, the N^(TM) fragment begins to accumulate in the streptavidin precipitated reaction. N^(TM) accumulation is paralleled by the appearance of the N^(EC) fragment, consistent with the contention that this fragment represents the extracellular domain of Notch and is tethered to the N^(TM) Notch polypeptide. It is concluded that Notch protein reaches the surface in a cleaved form and that newly synthesized full-length Notch is not found on the plasma membrane.

6.10 Notch Heterodimers Bind the Ligand Delta

The biological significance of the heterodimeric Notch form would be questionable if it could not bind ligands. Physical interaction between the extracellular domains of Notch and Delta have been demonstrated with the help of aggregation assays involving Delta and Notch expressing cells. If the heterodimeric form interacts with Delta after aggregation then the 110 kd N^(TM) fragment should co-immunoprecipitate using Delta antibodies. It was found that after aggregation, Delta antibodies are capable of efficiently immunoprecipitating the N^(TM) fragment demonstrating that the heterodimeric form can bind Delta (FIG. 8). As expected, if the aggregation is disrupted by depleting calcium from the medium by EGTA (Fehon et al., 1993, Cell 61:523-534). Delta antibodies fail to efficiently precipitate N^(TM) (data not shown).

6.11 Discussion

The strong structural conservation among both the Drosophila and vertebrate Notch gene products, and among homologs of other components of the same pathway, imply that the molecular and biochemical mechanisms involved in Notch signaling are conserved across species boundaries. The question of what particular roles are played by the assortment of paralogs within the Notch superfamily, in combination with the various paralogs of the other pathway components, remains unclear. Expression pattern comparisons, structural similarities and the available functional data for distinct paralogs suggest that these molecules possess different expression profiles but similar biochemical and developmental properties.

It has been found that the human Notch2 protein is a highly conserved member of the Notch protein family. Specific Notch EGF repeats have been implicated in protein interactions, and missense mutations in both Drosophila and humans have been associated with mutant phenotypes (Hartley et al., 1987, EMBO J. 6:3407-3417; Kelley et al., 1987, Cell 51:539-548; Rebay et al., 1991, Cell 67:687-699; Joutel et al., 1996, Nature 383:707-711). Functional data regarding the cysteine rich LN repeats are lacking. Nevertheless, all Notch homologs, from flies to humans, share similar LN repeat stretches in the equivalent extracellular region of the receptor. Within the intracellular domain of the Notch proteins, all six of the Ankyrin repeats are highly conserved. These repeats have been shown to play a crucial role in Notch signaling and have been implicated in molecular interactions between Drosophila Notch and the Deltex protein, which behaves as a positive regulator of Notch activity (Matsuno et al., 1995, Development 121:2633-2644), and with the downstream effector Suppressor of Hairless (Fortini and Artavanis-Tsakonas, 1994, Cell 79:273-282; Matsuno et al., 1995, Development 121:2633-2644). Consistent with the high degree of conservation, Notch2 Ankyrin repeats were found to interact both with Drosophila as well as with human Deltex (K. Matsuno and S. Artavanis-Tsakonas, unpublished observations).

The biochemical evidence presented herein shows that the Notch receptor is cleaved in the trans-Golgi network before reaching the cell surface. Pulse labeling experiments in combination with the biotinylation data indicate that the full-length Notch molecule does not reach the plasma membrane. The varying amounts of full-length Notch detected in different cell extracts presumably reflects a newly synthesized, inactive receptor that has not yet reached the Golgi and is inaccessible to ligands. Several lines of evidence indicate that this cleavage is a general property of cellular Notch. First, the same cleavage pattern is seen in all human cell lines and human tissues examined. Second, both Notch1 and Notch2 are processed in the same way. Third, the cleavage product N^(TM) is seen in both freshly prepared embryonic rat tissues as well as in Drosophila extracts.

The subcellular fractionation and biotinylation studies demonstrate that N^(TM) is associated with the plasma membrane, indicating a cleavage in the extracellular region of Notch. The epitope recognized by the antibodies used here was raised against the least conserved region of the intracellular domain mapping between the PEST sequence and the Ankyrin repeats (Zagouras et al., 1995, Proc. Natl. Acad. Sci. USA 92:6414-6418). Hence, N^(TM) must include the intracellular Notch2 sequences mapping between this C-terminal epitope and the transmembrane domain. It is likely the C. elegans Notch-like receptors lin-12 and glp-1 are cleaved in an analogous fashion, since N-terminal and C-terminal fragments of glp-1 were found to co-purify (Crittenden et al., 1994, Development 120:2901-2911). A deletion analysis involving Notch1 expression constructs transfected in cell lines by Aster et al., 1994, Cold Spring Harbor Symposia on Quantitative Biology 59:125-136, led them to suggest that, under their experimental conditions, Notch1 may be cleaved between the LN repeats and the transmembrane domain. It is noted that in the extracts examined herein, the main Notch1 Notch processing product in SJ-NB5 and HaCat cells is, as in Notch2, approximately 110 kD. In rat embryos, however, the main cleavage product appears to be larger. The significance of such qualitative differences in the processing pattern, or the additional breakdown products detected in our western blots, remains to be determined.

The accumulated evidence strongly indicates that N^(EC) contains the cleaved extracellular sequences of Notch, even though the lack of appropriate antibodies prevents one from directly demonstrating this hypothesis. The kinetics of N^(EC) accumulation and its inhibition profile are identical to N^(TM). The molecular weights of the Notch breakdown products, as argued above, are also compatible with such notion. Finally, the relative incorporation of radioactive cysteine in the two fragments reflects the approximately 10:1 ratio predicted by the amino acid composition of two fragments produced by a cleavage such that N^(EC) has most of the extracellular domain. In this regard, it is noteworthy that extracellular Notch fragments are present in the conditioned medium of Drosophila cell cultures that express Notch (Rebay, 1993, Ph.D. Thesis Yale University; I. Rebay, R. Fehon and S. Artavanis-Tsakonas, unpublished observations). Immunocytochemical studies with Drosophila tissues do not reveal differences in the cellular distribution of the intracellular vs. the extracellular domain of Notch (R. Fehon and S. Artavanis-Tsakonas, unpublished observations).

The co-precipitation of the N^(EC) fragment together with N^(TM), and the simultaneous appearance of the two fragments on the plasma membrane, indicate that N^(EC) and N^(TM) are tethered to one another. The inability to detect full-length Notch on the surface indicates that the cleaved form is the active form of the receptor.

Tethering of N^(TM) to N^(EC) is compatible with both the assumed mode of action of Notch, which necessitates interactions between the extracellular domains of the Notch receptor and its ligands, and with the cell autonomous nature of Notch signaling (Stern and Tokunaga, 1968, Proc. Natl. Acad. Sci. USA 60:1252-1259; Markopoulou et al., 1990, Journal of Experimental Zoology 27:23-27; Hoppe and Greenspan, 1990, Development 109:875-885; Heitzler and Simpson, 1991, Cell 64:1083-1092). On the other hand, any model of Notch biochemical activity and cellular function must take into account that Notch is cleaved. Several questions raised by this finding are worth pointing out. The possibility that N^(EC) may be released from the surface, acting as an inhibitor of the pathway, must be further examined, especially in view of reports that have appeared in the literature over the years suggesting that Notch may have non-autonomous activities (Gehring, 1973, In Genetic Mechanisms of Development: The 31st Symposium of the Society for Developmental Biology. (New York: Academic Press Inc.); Technau et al., 1987, Proc. Natl. Acad. Sci. USA:84, 4500-4504; Baker and Schubiger, 1996, Development 122:617-626). Such a scenario must take into account that the expression of truncated forms of Notch, approximately corresponding to the postulated structure of N^(TM), results in the constitutive activation of the receptor (Ellisen et al., 1991, Cell 66:649-661; Kopan et al., 1994, Development 120:2385-2396; Jennings et al., 1994, Development 120:3537-3548; Sun and Artavanis-Tsakonas, 1996, Development 122:2465-2474).

The notion that alterations in the extracellular domain may facilitate signaling events has been proposed on the basis of studies involving the expression of engineered constructs in cultured cells (Kopan et al., 1996, Proc. Natl. Acad. Sci. USA 93:1683-1688). Irrespective of how well these studies reflect the in vivo situation, together with the well documented in vivo action of truncated forms of Notch, they do raise the possibility that a ligand-dependent degradation or cleavage of the extracellular domain may result in the activation of the receptor. However, it seems unlikely that signaling would involve a simple ligand-dependent “shedding” of N^(EC). For instance, cell adhesion mediated by Notch/Ligand interactions has been shown to trigger an endocytic flow of Delta molecules in the Notch expressing cells, where it is eventually found in multivesicular bodies (Fehon et al., 1990, Cell 61:523-534; R. Fehon and S. Artavanis-Tsakonas, unpublished results). Detailed expression studies of Delta expression in cells known to undergo Notch signaling are consistent with the cell culture findings (Kooh et al., 1993, Development 117:493-507). At this stage it seems that the simplest working hypothesis on Notch signaling should involve the heterodimeric (N^(EC)/N^(TM)) surface Notch complex proposed here, rather than the action of any single cleaved fragment (see the proposed model in FIG. 9). The negative complementation displayed by the Abruptex mutation, a group of gain-of-function mutants affecting amino acids in the EGF homologous region of Notch, has been thought to reflect homotypic interactions between Notch receptors (Foster, 1975, Genetics 81:99-120; Xu et al., 1990, Genes Dev. 4:464-475). Therefore akin, for example, to the insulin receptor, the N^(EC)/N^(TM) heterodimer may be engaged in homotypic, or conceivably heterotypic, interactions. The analysis of the Notch receptor on nonreducing gels is consistent with this notion. In the absence of reducing agents, N^(EC) and N^(TM) are not detected. However, instead of detecting the full length molecule we detect higher molecular weight complexes of a yet undetermined nature (data not shown).

Since full-length Notch appears to reflect a ligand inaccessible, intracellular form of the protein, cleavage provides an important tool to regulate the Notch pathway. Such cleavage can effectively control the number of active surface receptors. Genetic analysis in Drosophila has demonstrated that the animal is unusually sensitive to the number of wild type copies of the Notch gene. In fact, Notch is one of a handful of genes in Drosophila that are both haplo insufficient as well as triplo mutant (Lindsley and Zimm, 1992, The genome of Drosophila melanogaster, (Academic Press, San Diego).

The present invention is not to be limited in scope by the specific embodiments described herein. Indeed, various modifications of the invention in addition to those described herein will become apparent to those skilled in the art from the foregoing description and accompanying figures. Such modifications are intended to fall within the scope of the appended claims.

Various publications are cited herein, the disclosures of which are incorporated by reference in their entireties.

4 1 2471 PRT Homo sapiens 1 Met Pro Ala Leu Arg Pro Ala Leu Leu Trp Ala Leu Leu Ala Leu Trp 1 5 10 15 Leu Cys Cys Ala Ala Pro Ala His Ala Leu Gln Cys Arg Asp Gly Tyr 20 25 30 Glu Pro Cys Val Asn Glu Gly Met Cys Val Thr Tyr His Asn Gly Thr 35 40 45 Gly Tyr Cys Lys Cys Pro Glu Gly Phe Leu Gly Glu Tyr Cys Gln His 50 55 60 Arg Asp Pro Cys Glu Lys Asn Arg Cys Gln Asn Gly Gly Thr Cys Val 65 70 75 80 Ala Gln Ala Met Leu Gly Lys Ala Thr Cys Arg Cys Ala Ser Gly Phe 85 90 95 Thr Gly Glu Asp Cys Gln Tyr Ser Thr Ser His Pro Cys Phe Val Ser 100 105 110 Arg Pro Cys Leu Asn Gly Gly Thr Cys His Met Leu Ser Arg Asp Thr 115 120 125 Tyr Glu Cys Thr Cys Gln Val Gly Phe Thr Gly Lys Glu Cys Gln Trp 130 135 140 Thr Asp Ala Cys Leu Ser His Pro Cys Ala Asn Gly Ser Thr Cys Thr 145 150 155 160 Thr Val Ala Asn Gln Phe Ser Cys Lys Cys Leu Thr Gly Phe Thr Gly 165 170 175 Gln Lys Cys Glu Thr Asp Val Asn Glu Cys Asp Ile Pro Gly His Cys 180 185 190 Gln His Gly Gly Thr Cys Leu Asn Leu Pro Gly Ser Tyr Gln Cys Gln 195 200 205 Cys Pro Gln Gly Phe Thr Gly Gln Tyr Cys Asp Ser Leu Tyr Val Pro 210 215 220 Cys Ala Pro Ser Pro Cys Val Asn Gly Gly Thr Cys Arg Gln Thr Gly 225 230 235 240 Asp Phe Thr Phe Glu Cys Asn Cys Leu Pro Gly Phe Glu Gly Ser Thr 245 250 255 Cys Glu Arg Asn Ile Asp Asp Cys Pro Asn His Arg Cys Gln Asn Gly 260 265 270 Gly Val Cys Val Asp Gly Val Asn Thr Tyr Asn Cys Arg Cys Pro Pro 275 280 285 Gln Trp Thr Gly Gln Phe Cys Thr Glu Asp Val Asp Glu Cys Leu Leu 290 295 300 Gln Pro Asn Ala Cys Gln Asn Gly Gly Thr Cys Ala Asn Arg Asn Gly 305 310 315 320 Gly Tyr Gly Cys Val Cys Val Asn Gly Trp Ser Gly Asp Asp Cys Ser 325 330 335 Glu Asn Ile Asp Asp Cys Ala Phe Ala Ser Cys Thr Pro Gly Ser Thr 340 345 350 Cys Ile Asp Arg Val Ala Ser Phe Ser Cys Met Cys Pro Glu Gly Lys 355 360 365 Ala Gly Leu Leu Cys His Leu Asp Asp Ala Cys Ile Ser Asn Pro Cys 370 375 380 His Lys Gly Ala Leu Cys Asp Thr Asn Pro Leu Asn Gly Gln Tyr Ile 385 390 395 400 Cys Thr Cys Pro Gln Gly Tyr Lys Gly Ala Asp Cys Thr Glu Asp Val 405 410 415 Asp Glu Cys Ala Met Ala Asn Ser Asn Pro Cys Glu His Ala Gly Lys 420 425 430 Cys Val Asn Thr Asp Gly Ala Phe His Cys Glu Cys Leu Lys Gly Tyr 435 440 445 Ala Gly Pro Arg Cys Glu Met Asp Ile Asn Glu Cys His Ser Asp Pro 450 455 460 Cys Gln Asn Asp Ala Thr Cys Leu Asp Lys Ile Gly Gly Phe Thr Cys 465 470 475 480 Leu Cys Met Pro Gly Phe Lys Gly Val His Cys Glu Leu Glu Ile Asn 485 490 495 Glu Cys Gln Ser Asn Pro Cys Val Asn Asn Gly Gln Cys Val Asp Lys 500 505 510 Val Asn Arg Phe Gln Cys Leu Cys Pro Pro Gly Phe Thr Gly Pro Val 515 520 525 Cys Gln Ile Asp Ile Asp Asp Cys Ser Ser Thr Pro Cys Leu Asn Gly 530 535 540 Ala Lys Cys Ile Asp His Pro Asn Gly Tyr Glu Cys Gln Cys Ala Thr 545 550 555 560 Gly Phe Thr Gly Val Leu Cys Glu Glu Asn Ile Asp Asn Cys Asp Pro 565 570 575 Asp Pro Cys His His Gly Gln Cys Gln Asp Gly Ile Asp Ser Tyr Thr 580 585 590 Cys Ile Cys Asn Pro Gly Tyr Met Gly Ala Ile Cys Ser Asp Gln Ile 595 600 605 Asp Glu Cys Tyr Ser Ser Pro Cys Leu Asn Asp Gly Arg Cys Ile Asp 610 615 620 Leu Val Asn Gly Tyr Gln Cys Asn Cys Gln Pro Gly Thr Ser Gly Val 625 630 635 640 Asn Cys Glu Ile Asn Phe Asp Asp Cys Ala Ser Asn Pro Cys Ile His 645 650 655 Gly Ile Cys Met Asp Gly Ile Asn Arg Tyr Ser Cys Val Cys Ser Pro 660 665 670 Gly Phe Thr Gly Gln Arg Cys Asn Ile Asp Ile Asp Glu Cys Ala Ser 675 680 685 Asn Pro Cys Arg Lys Gly Ala Thr Cys Ile Asn Gly Val Asn Gly Phe 690 695 700 Arg Cys Ile Cys Pro Glu Gly Pro His His Pro Ser Cys Tyr Ser Gln 705 710 715 720 Val Asn Glu Cys Leu Ser Asn Pro Cys Ile His Gly Asn Cys Thr Gly 725 730 735 Gly Leu Ser Gly Tyr Lys Cys Leu Cys Asp Ala Gly Trp Val Gly Ile 740 745 750 Asn Cys Glu Val Asp Lys Asn Glu Cys Leu Ser Asn Pro Cys Gln Asn 755 760 765 Gly Gly Thr Cys Asp Asn Leu Val Asn Gly Tyr Arg Cys Thr Cys Lys 770 775 780 Lys Gly Phe Lys Gly Tyr Asn Cys Gln Val Asn Ile Asp Glu Cys Ala 785 790 795 800 Ser Asn Pro Cys Leu Asn Gln Gly Thr Cys Phe Asp Asp Ile Ser Gly 805 810 815 Tyr Thr Cys His Cys Val Leu Pro Tyr Thr Gly Lys Asn Cys Gln Thr 820 825 830 Val Leu Ala Pro Cys Ser Pro Asn Pro Cys Glu Asn Ala Ala Val Cys 835 840 845 Lys Glu Ser Pro Asn Phe Glu Ser Tyr Thr Cys Leu Cys Ala Pro Gly 850 855 860 Trp Gln Gly Gln Arg Cys Thr Ile Asp Ile Asp Glu Cys Ile Ser Lys 865 870 875 880 Pro Cys Met Asn His Gly Leu Cys His Asn Thr Gln Gly Ser Tyr Met 885 890 895 Cys Glu Cys Pro Pro Gly Phe Ser Gly Met Asp Cys Glu Glu Asp Ile 900 905 910 Asp Asp Cys Leu Ala Asn Pro Cys Gln Asn Gly Gly Ser Cys Met Asp 915 920 925 Gly Val Asn Thr Phe Ser Cys Leu Cys Leu Pro Gly Phe Thr Gly Asp 930 935 940 Lys Cys Gln Thr Asp Met Asn Glu Cys Leu Ser Glu Pro Cys Lys Asn 945 950 955 960 Gly Gly Thr Cys Ser Asp Tyr Val Asn Ser Tyr Thr Cys Lys Cys Gln 965 970 975 Ala Gly Phe Asp Gly Val His Cys Glu Asn Asn Ile Asn Glu Cys Thr 980 985 990 Glu Ser Ser Cys Phe Asn Gly Gly Thr Cys Val Asp Gly Ile Asn Ser 995 1000 1005 Phe Ser Cys Leu Cys Pro Val Gly Phe Thr Gly Ser Phe Cys Leu His 1010 1015 1020 Glu Ile Asn Glu Cys Ser Ser His Pro Cys Leu Asn Glu Gly Thr Cys 1025 1030 1035 1040 Val Asp Gly Leu Gly Thr Tyr Arg Cys Ser Cys Pro Leu Gly Tyr Thr 1045 1050 1055 Gly Lys Asn Cys Gln Thr Leu Val Asn Leu Cys Ser Arg Ser Pro Cys 1060 1065 1070 Lys Asn Lys Gly Thr Cys Val Gln Lys Lys Ala Glu Ser Gln Cys Leu 1075 1080 1085 Cys Pro Ser Gly Trp Ala Gly Ala Tyr Cys Asp Val Pro Asn Val Ser 1090 1095 1100 Cys Asp Ile Ala Ala Ser Arg Arg Gly Val Leu Val Glu His Leu Cys 1105 1110 1115 1120 Gln His Ser Gly Val Cys Ile Asn Ala Gly Asn Thr His Tyr Cys Gln 1125 1130 1135 Cys Pro Leu Gly Tyr Thr Gly Ser Tyr Cys Glu Glu Gln Leu Asp Glu 1140 1145 1150 Cys Ala Ser Asn Pro Cys Gln His Gly Ala Thr Cys Ser Asp Phe Ile 1155 1160 1165 Gly Gly Tyr Arg Cys Glu Cys Val Pro Gly Tyr Gln Gly Val Asn Cys 1170 1175 1180 Glu Tyr Glu Val Asp Glu Cys Gln Asn Gln Pro Cys Gln Asn Gly Gly 1185 1190 1195 1200 Thr Cys Ile Asp Leu Val Asn His Phe Lys Cys Ser Cys Pro Pro Gly 1205 1210 1215 Thr Arg Gly Leu Leu Cys Glu Glu Asn Ile Asp Asp Cys Ala Arg Gly 1220 1225 1230 Pro His Cys Leu Asn Gly Gly Gln Cys Met Asp Arg Ile Gly Gly Tyr 1235 1240 1245 Ser Cys Arg Cys Leu Pro Gly Phe Ala Gly Glu Arg Cys Glu Gly Asp 1250 1255 1260 Ile Asn Glu Cys Leu Ser Asn Pro Cys Ser Ser Glu Gly Ser Leu Asp 1265 1270 1275 1280 Cys Ile Gln Leu Thr Asn Asp Tyr Leu Cys Val Cys Arg Ser Ala Phe 1285 1290 1295 Thr Gly Arg His Cys Glu Thr Phe Val Asp Val Cys Pro Gln Met Pro 1300 1305 1310 Cys Leu Asn Gly Gly Thr Cys Ala Val Ala Ser Asn Met Pro Asp Gly 1315 1320 1325 Phe Ile Cys Arg Cys Pro Pro Gly Phe Ser Gly Ala Arg Cys Gln Ser 1330 1335 1340 Ser Cys Gly Gln Val Lys Cys Arg Lys Gly Glu Gln Cys Val His Thr 1345 1350 1355 1360 Ala Ser Gly Pro Arg Cys Phe Cys Pro Ser Pro Arg Asp Cys Glu Ser 1365 1370 1375 Gly Cys Ala Ser Ser Pro Cys Gln His Gly Gly Ser Cys His Pro Gln 1380 1385 1390 Arg Gln Pro Pro Tyr Tyr Ser Cys Gln Cys Ala Pro Pro Phe Ser Gly 1395 1400 1405 Ser Arg Cys Glu Leu Tyr Thr Ala Pro Pro Ser Thr Pro Pro Ala Thr 1410 1415 1420 Cys Leu Ser Gln Tyr Cys Ala Asp Lys Ala Arg Asp Gly Val Cys Asp 1425 1430 1435 1440 Glu Ala Cys Asn Ser His Ala Cys Gln Trp Asp Gly Gly Asp Cys Ser 1445 1450 1455 Leu Thr Met Glu Asn Pro Trp Ala Asn Cys Ser Ser Pro Leu Pro Cys 1460 1465 1470 Trp Asp Tyr Ile Asn Asn Gln Cys Asp Glu Leu Cys Asn Thr Val Glu 1475 1480 1485 Cys Leu Phe Asp Asn Phe Glu Cys Gln Gly Asn Ser Lys Thr Cys Lys 1490 1495 1500 Tyr Asp Lys Tyr Cys Ala Asp His Phe Lys Asp Asn His Cys Asn Gln 1505 1510 1515 1520 Gly Cys Asn Ser Glu Glu Cys Gly Trp Asp Gly Leu Asp Cys Ala Ala 1525 1530 1535 Asp Gln Pro Glu Asn Leu Ala Glu Gly Thr Leu Val Ile Val Val Leu 1540 1545 1550 Met Pro Pro Glu Gln Leu Leu Gln Asp Ala Arg Ser Phe Leu Arg Ala 1555 1560 1565 Leu Gly Thr Leu Leu His Thr Asn Leu Arg Ile Lys Arg Asp Ser Gln 1570 1575 1580 Gly Glu Leu Met Val Tyr Pro Tyr Tyr Gly Glu Lys Ser Ala Ala Met 1585 1590 1595 1600 Lys Lys Gln Arg Met Thr Arg Arg Ser Leu Pro Gly Glu Gln Glu Gln 1605 1610 1615 Glu Val Ala Gly Ser Lys Val Phe Leu Glu Ile Asp Asn Arg Gln Cys 1620 1625 1630 Val Gln Asp Ser Asp His Cys Phe Lys Asn Thr Asp Ala Ala Ala Ala 1635 1640 1645 Leu Leu Ala Ser His Ala Ile Gln Gly Thr Leu Ser Tyr Pro Leu Val 1650 1655 1660 Ser Val Val Ser Glu Ser Leu Thr Pro Glu Arg Thr Gln Leu Leu Tyr 1665 1670 1675 1680 Leu Leu Ala Val Ala Val Val Ile Ile Leu Phe Ile Ile Leu Leu Gly 1685 1690 1695 Val Ile Met Ala Lys Arg Lys Arg Lys His Gly Ser Leu Trp Leu Pro 1700 1705 1710 Glu Gly Phe Thr Leu Arg Arg Asp Ala Ser Asn His Lys Arg Arg Glu 1715 1720 1725 Pro Val Gly Gln Asp Ala Val Gly Leu Lys Asn Leu Ser Val Gln Val 1730 1735 1740 Ser Glu Ala Asn Leu Ile Gly Thr Gly Thr Ser Glu His Trp Val Asp 1745 1750 1755 1760 Asp Glu Gly Pro Gln Pro Lys Lys Val Lys Ala Glu Asp Glu Ala Leu 1765 1770 1775 Leu Ser Glu Glu Asp Asp Pro Ile Asp Arg Arg Pro Trp Thr Gln Gln 1780 1785 1790 His Leu Glu Ala Ala Asp Ile Arg Arg Thr Pro Ser Leu Ala Leu Thr 1795 1800 1805 Pro Pro Gln Ala Glu Gln Glu Val Asp Val Leu Asp Val Asn Val Arg 1810 1815 1820 Gly Pro Asp Gly Cys Thr Pro Leu Met Leu Ala Ser Leu Arg Gly Gly 1825 1830 1835 1840 Ser Ser Asp Leu Ser Asp Glu Asp Glu Asp Ala Glu Asp Ser Ser Ala 1845 1850 1855 Asn Ile Ile Thr Asp Leu Val Tyr Gln Gly Ala Ser Leu Gln Ala Gln 1860 1865 1870 Thr Asp Arg Thr Gly Glu Met Ala Leu His Leu Ala Ala Arg Tyr Ser 1875 1880 1885 Arg Ala Asp Ala Ala Lys Arg Leu Leu Asp Ala Gly Ala Asp Ala Asn 1890 1895 1900 Ala Gln Asp Asn Met Gly Arg Cys Pro Leu His Ala Ala Val Ala Ala 1905 1910 1915 1920 Asp Ala Gln Gly Val Phe Gln Ile Leu Ile Arg Asn Arg Val Thr Asp 1925 1930 1935 Leu Asp Ala Arg Met Asn Asp Gly Thr Thr Pro Leu Ile Leu Ala Ala 1940 1945 1950 Arg Leu Ala Val Glu Gly Met Val Ala Glu Leu Ile Asn Cys Gln Ala 1955 1960 1965 Asp Val Asn Ala Val Asp Asp His Gly Lys Ser Ala Leu His Trp Ala 1970 1975 1980 Ala Ala Val Asn Asn Val Glu Ala Thr Leu Leu Leu Leu Lys Asn Gly 1985 1990 1995 2000 Ala Asn Arg Asp Met Gln Asp Asn Lys Glu Glu Thr Pro Leu Phe Leu 2005 2010 2015 Ala Ala Arg Glu Gly Ser Tyr Glu Ala Ala Lys Ile Leu Leu Asp His 2020 2025 2030 Phe Ala Asn Arg Asp Ile Thr Asp His Met Asp Arg Leu Pro Arg Asp 2035 2040 2045 Val Ala Arg Asp Arg Met His His Asp Ile Val Arg Leu Leu Asp Glu 2050 2055 2060 Tyr Asn Val Thr Pro Ser Pro Pro Gly Thr Val Leu Thr Ser Ala Leu 2065 2070 2075 2080 Ser Pro Val Ile Cys Gly Pro Asn Arg Ser Phe Leu Ser Leu Lys His 2085 2090 2095 Thr Pro Met Gly Lys Lys Ser Arg Arg Pro Ser Ala Lys Ser Thr Met 2100 2105 2110 Pro Thr Ser Leu Pro Asn Leu Ala Lys Glu Ala Lys Asp Ala Lys Gly 2115 2120 2125 Ser Arg Arg Lys Lys Ser Leu Ser Glu Lys Val Gln Leu Ser Glu Ser 2130 2135 2140 Ser Val Thr Leu Ser Pro Val Asp Ser Leu Glu Ser Pro His Thr Tyr 2145 2150 2155 2160 Val Ser Asp Thr Thr Ser Ser Pro Met Ile Thr Ser Pro Gly Ile Leu 2165 2170 2175 Gln Ala Ser Pro Asn Pro Met Leu Ala Thr Ala Ala Pro Pro Ala Pro 2180 2185 2190 Val His Ala Gln His Ala Leu Ser Phe Ser Asn Leu His Glu Met Gln 2195 2200 2205 Pro Leu Ala His Gly Ala Ser Thr Val Leu Pro Ser Val Ser Gln Leu 2210 2215 2220 Leu Ser His His His Ile Val Ser Pro Gly Ser Gly Ser Ala Gly Ser 2225 2230 2235 2240 Leu Ser Arg Leu His Pro Val Pro Val Pro Ala Asp Trp Met Asn Arg 2245 2250 2255 Met Glu Val Asn Glu Thr Gln Tyr Asn Glu Met Phe Gly Met Val Leu 2260 2265 2270 Ala Pro Ala Glu Gly Thr His Pro Gly Ile Ala Pro Gln Ser Arg Pro 2275 2280 2285 Pro Glu Gly Lys His Ile Thr Thr Pro Arg Glu Pro Leu Pro Pro Ile 2290 2295 2300 Val Thr Phe Gln Leu Ile Pro Lys Gly Ser Ile Ala Gln Pro Ala Gly 2305 2310 2315 2320 Ala Pro Gln Pro Gln Ser Thr Cys Pro Pro Ala Val Ala Gly Pro Leu 2325 2330 2335 Pro Thr Met Tyr Gln Ile Pro Glu Met Ala Arg Leu Pro Ser Val Ala 2340 2345 2350 Phe Pro Thr Ala Met Met Pro Gln Gln Asp Gly Gln Val Ala Gln Thr 2355 2360 2365 Ile Leu Pro Ala Tyr His Pro Phe Pro Ala Ser Val Gly Lys Tyr Pro 2370 2375 2380 Thr Pro Pro Ser Gln His Ser Tyr Ala Ser Ser Asn Ala Ala Glu Arg 2385 2390 2395 2400 Thr Pro Ser His Ser Gly His Leu Gln Gly Glu His Pro Tyr Leu Thr 2405 2410 2415 Pro Ser Pro Glu Ser Pro Asp Gln Trp Ser Ser Ser Ser Pro His Ser 2420 2425 2430 Ala Ser Asp Trp Ser Asp Val Thr Thr Ser Pro Thr Pro Gly Gly Ala 2435 2440 2445 Gly Gly Gly Gln Arg Gly Pro Gly Thr His Met Ser Glu Pro Pro His 2450 2455 2460 Asn Asn Met Gln Val Tyr Ala 2465 2470 2 2556 PRT Homo sapiens 2 Met Pro Pro Leu Leu Ala Pro Leu Leu Cys Leu Ala Leu Leu Pro Ala 1 5 10 15 Leu Ala Ala Arg Gly Pro Arg Cys Ser Gln Pro Gly Glu Thr Cys Leu 20 25 30 Asn Gly Gly Lys Cys Glu Ala Ala Asn Gly Thr Glu Ala Cys Val Cys 35 40 45 Gly Gly Ala Phe Val Gly Pro Arg Cys Gln Asp Pro Asn Pro Cys Leu 50 55 60 Ser Thr Pro Cys Lys Asn Ala Gly Thr Cys His Val Val Asp Arg Arg 65 70 75 80 Gly Val Ala Asp Tyr Ala Cys Ser Cys Ala Leu Gly Phe Ser Gly Pro 85 90 95 Leu Cys Leu Thr Pro Leu Asp Asn Ala Cys Leu Thr Asn Pro Cys Arg 100 105 110 Asn Gly Gly Thr Cys Asp Leu Leu Thr Leu Thr Glu Tyr Lys Cys Arg 115 120 125 Cys Pro Pro Gly Trp Ser Gly Lys Ser Cys Gln Gln Ala Asp Pro Cys 130 135 140 Ala Ser Asn Pro Cys Ala Asn Gly Gly Gln Cys Leu Pro Phe Glu Ala 145 150 155 160 Ser Tyr Ile Cys His Cys Pro Pro Ser Phe His Gly Pro Thr Cys Trp 165 170 175 Gln Asp Val Asn Glu Cys Gly Gln Lys Pro Arg Leu Cys Arg His Gly 180 185 190 Gly Thr Cys His Asn Glu Val Gly Ser Tyr Arg Cys Val Cys Arg Ala 195 200 205 Thr His Thr Gly Pro Asn Cys Glu Trp Pro Tyr Val Pro Cys Ser Pro 210 215 220 Ser Pro Cys Gln Asn Gly Gly Thr Cys Arg Pro Thr Gly Asp Val Thr 225 230 235 240 His Glu Cys Ala Cys Leu Pro Gly Phe Thr Gly Gln Asn Cys Glu Glu 245 250 255 Asn Ile Asp Asp Cys Pro Gly Asn Asn Cys Lys Asn Gly Gly Ala Cys 260 265 270 Val Asp Gly Val Asn Thr Tyr Asn Cys Pro Cys Pro Pro Glu Trp Thr 275 280 285 Gly Gln Tyr Cys Thr Glu Asp Val Asp Glu Cys Gln Leu Met Pro Asn 290 295 300 Ala Cys Gln Asn Gly Gly Thr Cys His Asn Thr His Gly Gly Tyr Asn 305 310 315 320 Cys Val Cys Val Asn Gly Trp Thr Gly Glu Asp Cys Ser Glu Asn Ile 325 330 335 Asp Asp Cys Ala Ser Ala Ala Cys Phe His Gly Ala Thr Cys His Asp 340 345 350 Arg Val Ala Ser Phe Tyr Cys Glu Cys Pro His Gly Arg Thr Gly Leu 355 360 365 Leu Cys His Leu Asn Asp Ala Cys Ile Ser Asn Pro Cys Asn Glu Gly 370 375 380 Ser Asn Cys Asp Thr Asn Pro Val Asn Gly Lys Ala Ile Cys Thr Cys 385 390 395 400 Pro Ser Gly Tyr Thr Gly Pro Ala Cys Ser Gln Asp Val Asp Glu Cys 405 410 415 Ser Leu Gly Ala Asn Pro Cys Glu His Ala Gly Lys Cys Ile Asn Thr 420 425 430 Leu Gly Ser Phe Glu Cys Gln Cys Leu Gln Gly Tyr Thr Gly Pro Arg 435 440 445 Cys Glu Ile Asp Val Asn Glu Cys Val Ser Asn Pro Cys Gln Asn Asp 450 455 460 Ala Thr Cys Leu Asp Gln Ile Gly Glu Phe Gln Cys Met Cys Met Pro 465 470 475 480 Gly Tyr Glu Gly Val His Cys Glu Val Asn Thr Asp Glu Cys Ala Ser 485 490 495 Ser Pro Cys Leu His Asn Gly Arg Cys Leu Asp Lys Ile Asn Glu Phe 500 505 510 Gln Cys Glu Cys Pro Thr Gly Phe Thr Gly His Leu Cys Gln Tyr Asp 515 520 525 Val Asp Glu Cys Ala Ser Thr Pro Cys Lys Asn Gly Ala Lys Cys Leu 530 535 540 Asp Gly Pro Asn Thr Tyr Thr Cys Val Cys Thr Glu Gly Tyr Thr Gly 545 550 555 560 Thr His Cys Glu Val Asp Ile Asp Glu Cys Asp Pro Asp Pro Cys His 565 570 575 Tyr Gly Ser Cys Lys Asp Gly Val Ala Thr Phe Thr Cys Leu Cys Arg 580 585 590 Pro Gly Tyr Thr Gly His His Cys Glu Thr Asn Ile Asn Glu Cys Ser 595 600 605 Ser Gln Pro Cys Arg Leu Trp Gly Thr Cys Gln Asp Pro Asp Asn Ala 610 615 620 Tyr Leu Cys Phe Cys Leu Lys Gly Thr Thr Gly Pro Asn Cys Glu Ile 625 630 635 640 Asn Leu Asp Asp Cys Ala Ser Ser Pro Cys Asp Ser Gly Thr Cys Leu 645 650 655 Asp Lys Ile Asp Gly Tyr Glu Cys Ala Cys Glu Pro Gly Tyr Thr Gly 660 665 670 Ser Met Cys Asn Ser Asn Ile Asp Glu Cys Ala Gly Asn Pro Cys His 675 680 685 Asn Gly Gly Thr Cys Glu Asp Gly Ile Asn Gly Phe Thr Cys Arg Cys 690 695 700 Pro Glu Gly Tyr His Asp Pro Thr Cys Leu Ser Glu Val Asn Glu Cys 705 710 715 720 Asn Ser Asn Pro Cys Val His Gly Ala Cys Trp Asp Ser Leu Asn Gly 725 730 735 Tyr Lys Cys Asp Cys Asp Pro Gly Trp Ser Gly Thr Asn Cys Asp Ile 740 745 750 Asn Asn Asn Glu Cys Glu Ser Asn Pro Cys Val Asn Gly Gly Thr Cys 755 760 765 Lys Asp Met Thr Ser Gly Ile Val Cys Thr Cys Trp Glu Gly Phe Ser 770 775 780 Gly Pro Asn Cys Gln Thr Asn Ile Asn Glu Cys Ala Ser Asn Pro Cys 785 790 795 800 Leu Asn Lys Gly Thr Cys Ile Asp Asp Val Ala Gly Tyr Lys Cys Asn 805 810 815 Cys Leu Leu Pro Tyr Thr Gly Ala Thr Cys Glu Val Val Leu Ala Pro 820 825 830 Cys Ala Pro Ser Pro Cys Arg Asn Gly Gly Glu Cys Arg Gln Ser Glu 835 840 845 Asp Tyr Glu Ser Phe Ser Cys Val Cys Pro Thr Ala Gly Ala Lys Gly 850 855 860 Gln Thr Cys Glu Val Asp Ile Asn Glu Cys Val Leu Ser Pro Cys Trp 865 870 875 880 His Gly Ala Ser Cys Gln Asn Thr His Gly Xaa Tyr Arg Cys His Cys 885 890 895 Gln Ala Gly Tyr Ser Gly Arg Asn Cys Glu Thr Asp Ile Asp Asp Cys 900 905 910 Trp Pro Asn Pro Cys His Asn Gly Gly Ser Cys Thr Asp Gly Ile Asn 915 920 925 Thr Ala Phe Cys Asp Cys Leu Pro Gly Phe Trp Gly Thr Phe Cys Glu 930 935 940 Glu Asp Ile Asn Glu Cys Ala Ser Asp Pro Cys Arg Asn Gly Ala Asn 945 950 955 960 Cys Thr Asp Cys Val Asp Ser Tyr Thr Cys Thr Cys Pro Ala Gly Phe 965 970 975 Ser Gly Ile His Cys Glu Asn Asn Thr Pro Asp Cys Thr Glu Ser Ser 980 985 990 Cys Phe Asn Gly Gly Thr Cys Val Asp Gly Ile Asn Ser Phe Thr Cys 995 1000 1005 Leu Cys Pro Pro Gly Phe Thr Gly Ser Tyr Cys Gln His Val Val Asn 1010 1015 1020 Glu Cys Asp Ser Arg Pro Cys Leu Leu Gly Gly Thr Cys Gln Asp Gly 1025 1030 1035 1040 Arg Gly Leu His Arg Cys Thr Cys Pro Gln Gly Tyr Thr Gly Pro Asn 1045 1050 1055 Cys Gln Asn Leu Val His Trp Cys Asp Ser Ser Pro Cys Lys Asn Gly 1060 1065 1070 Gly Lys Cys Trp Gln Thr His Thr Gln Tyr Arg Cys Glu Cys Pro Ser 1075 1080 1085 Gly Trp Thr Gly Leu Tyr Cys Asp Val Pro Ser Val Ser Cys Glu Val 1090 1095 1100 Ala Ala Gln Arg Gln Gly Val Asp Val Ala Arg Leu Cys Gln His Gly 1105 1110 1115 1120 Gly Leu Cys Val Asp Ala Gly Asn Thr His His Cys Arg Cys Gln Ala 1125 1130 1135 Gly Tyr Thr Gly Ser Tyr Cys Glu Asp Leu Val Asp Glu Cys Ser Pro 1140 1145 1150 Ser Pro Cys Gln Asn Gly Ala Thr Cys Thr Asp Tyr Leu Gly Gly Tyr 1155 1160 1165 Ser Cys Lys Cys Val Ala Gly Tyr His Gly Val Asn Cys Ser Glu Glu 1170 1175 1180 Ile Asp Glu Cys Leu Ser His Pro Cys Gln Asn Gly Gly Thr Cys Leu 1185 1190 1195 1200 Asp Leu Pro Asn Thr Tyr Lys Cys Ser Cys Pro Trp Gly Thr Gln Gly 1205 1210 1215 Val His Cys Glu Ile Asn Val Asp Asp Cys Asn Pro Pro Val Asp Pro 1220 1225 1230 Val Ser Trp Ser Pro Lys Cys Phe Asn Asn Gly Thr Cys Val Asp Gln 1235 1240 1245 Val Gly Gly Tyr Ser Cys Thr Cys Pro Pro Gly Phe Val Gly Glu Arg 1250 1255 1260 Cys Glu Gly Asp Val Asn Glu Cys Leu Ser Asn Pro Cys Asp Ala Arg 1265 1270 1275 1280 Gly Thr Gln Asn Cys Val Gln Arg Val Asn Asp Phe His Cys Glu Cys 1285 1290 1295 Arg Ala Gly His Thr Gly Arg Arg Cys Glu Ser Val Ile Asn Gly Cys 1300 1305 1310 Lys Gly Lys Pro Cys Lys Asn Gly Gly Thr Cys Ala Val Ala Ser Asn 1315 1320 1325 Thr Ala Arg Gly Phe Ile Cys Lys Cys Pro Ala Gly Phe Glu Gly Ala 1330 1335 1340 Thr Cys Glu Asn Asp Ala Arg Thr Cys Gly Ser Leu Arg Cys Leu Asn 1345 1350 1355 1360 Gly Gly Thr Cys Ile Ser Gly Pro Arg Ser Pro Thr Cys Leu Cys Leu 1365 1370 1375 Gly Pro Phe Thr Gly Pro Glu Cys Gln Phe Pro Ala Ser Ser Pro Cys 1380 1385 1390 Leu Gly Gly Asn Pro Cys Tyr Asn Gln Gly Thr Cys Glu Pro Thr Ser 1395 1400 1405 Glu Ser Pro Phe Tyr Arg Cys Leu Cys Pro Ala Lys Phe Asn Gly Leu 1410 1415 1420 Leu Cys His Ile Leu Asp Tyr Ser Phe Gly Gly Gly Ala Gly Arg Asp 1425 1430 1435 1440 Ile Pro Pro Pro Leu Ile Glu Glu Ala Cys Glu Leu Pro Glu Cys Gln 1445 1450 1455 Glu Asp Ala Gly Asn Lys Val Cys Ser Leu Gln Cys Asn Asn His Ala 1460 1465 1470 Cys Gly Trp Asp Gly Gly Asp Cys Ser Leu Asn Phe Asn Asp Pro Trp 1475 1480 1485 Lys Asn Cys Thr Gln Ser Leu Gln Cys Trp Lys Tyr Phe Ser Asp Gly 1490 1495 1500 His Cys Asp Ser Gln Cys Asn Ser Ala Gly Cys Leu Phe Asp Gly Phe 1505 1510 1515 1520 Asp Cys Gln Arg Ala Glu Gly Gln Cys Asn Pro Leu Tyr Asp Gln Tyr 1525 1530 1535 Cys Lys Asp His Phe Ser Asp Gly His Cys Asp Gln Gly Cys Asn Ser 1540 1545 1550 Ala Glu Cys Glu Trp Asp Gly Leu Asp Cys Ala Glu His Val Pro Glu 1555 1560 1565 Arg Leu Ala Ala Gly Thr Leu Val Val Val Val Leu Met Pro Pro Glu 1570 1575 1580 Gln Leu Arg Asn Ser Ser Phe His Phe Leu Trp Glu Leu Ser Arg Val 1585 1590 1595 1600 Leu His Thr Asn Val Val Phe Lys Arg Asp Ala His Gly Gln Gln Met 1605 1610 1615 Ile Phe Pro Tyr Tyr Gly Arg Glu Glu Glu Leu Arg Lys His Pro Ile 1620 1625 1630 Lys Arg Ala Ala Glu Gly Trp Ala Ala Pro Asp Ala Leu Leu Gly Gln 1635 1640 1645 Val Lys Ala Ser Leu Leu Pro Gly Gly Ser Glu Gly Gly Trp Trp Trp 1650 1655 1660 Arg Glu Leu Asp Pro Met Asp Val Arg Gly Ser Ile Val Tyr Leu Glu 1665 1670 1675 1680 Ile Asp Asn Trp Gln Cys Val Gln Ala Ser Ser Gln Cys Phe Gln Ser 1685 1690 1695 Ala Thr Asp Val Ala Ala Phe Leu Gly Ala Leu Ala Ser Leu Gly Ser 1700 1705 1710 Leu Asn Ile Pro Tyr Lys Ile Glu Ala Val Gln Ser Glu Thr Val Glu 1715 1720 1725 Pro Pro Pro Pro Ala Gln Leu His Phe Met Tyr Val Ala Ala Ala Ala 1730 1735 1740 Phe Val Leu Leu Phe Phe Val Gly Cys Gly Val Leu Leu Ser Arg Lys 1745 1750 1755 1760 Arg Trp Xaa Gln His Gly Gln Leu Trp Phe Pro Glu Gly Phe Lys Val 1765 1770 1775 Ser Glu Ala Ser Lys Lys Lys Trp Trp Glu Xaa Leu Gly Glu Asp Ser 1780 1785 1790 Val Gly Leu Lys Pro Leu Lys Asn Ala Ser Asp Gly Ala Leu Met Asp 1795 1800 1805 Asp Asn Gln Asn Glu Trp Gly Asp Glu Asp Leu Glu Thr Lys Lys Phe 1810 1815 1820 Trp Phe Glu Glu Pro Val Val Leu Pro Asp Leu Asp Asp Gln Thr Asp 1825 1830 1835 1840 His Trp Gln Trp Thr Gln Gln His Leu Asp Ala Ala Asp Leu Arg Met 1845 1850 1855 Ser Ala Met Ala Pro Thr Pro Pro Gln Gly Glu Val Asp Ala Asp Cys 1860 1865 1870 Met Asp Val Asn Val Arg Gly Pro Asp Gly Phe Thr Pro Leu Met Ile 1875 1880 1885 Ala Ser Cys Ser Gly Gly Gly Leu Glu Thr Gly Asn Ser Glu Glu Glu 1890 1895 1900 Glu Asp Ala Pro Ala Val Ile Ser Asp Phe Ile Tyr Gln Gly Ala Ser 1905 1910 1915 1920 Leu His Asn Gln Thr Asp Arg Thr Gly Glu Thr Ala Leu His Leu Ala 1925 1930 1935 Ala Arg Tyr Ser Arg Ser Asp Ala Ala Lys Arg Leu Leu Glu Ala Ser 1940 1945 1950 Ala Asp Ala Asn Ile Gln Asp Asn Met Gly Arg Thr Pro Leu His Ala 1955 1960 1965 Ala Val Ser Ala Asp Ala Gln Gly Val Phe Gln Ile Leu Ile Trp Asn 1970 1975 1980 Arg Ala Thr Asp Leu Asp Ala Arg Met His Asp Gly Thr Thr Pro Leu 1985 1990 1995 2000 Ile Leu Ala Ala Arg Leu Ala Val Glu Gly Met Leu Glu Asp Leu Ile 2005 2010 2015 Asn Ser His Ala Asp Val Asn Ala Val Asp Asp Leu Gly Lys Ser Ala 2020 2025 2030 Leu His Trp Ala Ala Ala Val Asn Asn Val Asp Ala Ala Val Val Leu 2035 2040 2045 Leu Lys Asn Gly Ala Asn Lys Asp Met Gln Asn Asn Arg Glu Glu Thr 2050 2055 2060 Pro Leu Phe Leu Ala Ala Trp Glu Gly Ser Tyr Glu Thr Ala Lys Val 2065 2070 2075 2080 Leu Leu Asp His Phe Ala Asn Trp Asp Ile Thr Asp His Met Asp Arg 2085 2090 2095 Leu Pro Arg Asp Ile Ala Gln Glu Arg Met His His Asp Ile Val Arg 2100 2105 2110 Leu Leu Asp Glu Tyr Asn Leu Val Arg Ser Pro Gln Leu His Gly Ala 2115 2120 2125 Pro Leu Gly Gly Thr Pro Thr Leu Ser Pro Pro Leu Cys Ser Pro Asn 2130 2135 2140 Gly Tyr Leu Gly Ser Leu Lys Pro Gly Val Gln Gly Lys Lys Val Arg 2145 2150 2155 2160 Lys Pro Ser Ser Lys Gly Leu Ala Cys Gly Ser Lys Glu Ala Lys Asp 2165 2170 2175 Leu Lys Ala Trp Arg Lys Lys Ser Gln Asp Gly Lys Gly Cys Leu Leu 2180 2185 2190 Asp Ser Ser Gly Met Leu Ser Pro Val Asp Ser Leu Glu Ser Pro His 2195 2200 2205 Gly Tyr Leu Ser Asp Val Ala Ser Pro Pro Leu Leu Pro Ser Pro Phe 2210 2215 2220 Gln Gln Ser Pro Ser Val Pro Leu Asn His Leu Pro Gly Met Pro Asp 2225 2230 2235 2240 Thr His Leu Gly Ile Gly His Leu Asn Val Ala Ala Lys Pro Glu Met 2245 2250 2255 Ala Ala Leu Gly Gly Gly Gly Trp Leu Ala Phe Glu Thr Gly Pro Pro 2260 2265 2270 Arg Leu Ser His Leu Pro Val Ala Ser Gly Thr Ser Thr Val Leu Gly 2275 2280 2285 Ser Ser Ser Gly Gly Ala Leu Asn Phe Thr Val Gly Gly Ser Thr Ser 2290 2295 2300 Leu Asn Gly Gln Cys Glu Trp Leu Ser Trp Leu Gln Ser Gly Met Val 2305 2310 2315 2320 Pro Asn Gln Tyr Asn Pro Leu Trp Gly Ser Val Ala Pro Gly Pro Leu 2325 2330 2335 Ser Thr Gln Ala Pro Ser Leu Gln His Gly Met Val Gly Pro Leu His 2340 2345 2350 Ser Ser Leu Ala Ala Ser Ala Leu Ser Gln Met Met Ser Tyr Gln Gly 2355 2360 2365 Leu Pro Ser Thr Trp Leu Ala Thr Gln Pro His Leu Val Gln Thr Gln 2370 2375 2380 Gln Val Gln Pro Gln Asn Leu Gln Met Gln Gln Gln Asn Leu Gln Pro 2385 2390 2395 2400 Ala Asn Ile Gln Gln Gln Gln Ser Leu Gln Pro Pro Pro Pro Pro Pro 2405 2410 2415 Gln Pro His Leu Gly Val Ser Ser Ala Ala Ser Gly His Leu Gly Trp 2420 2425 2430 Ser Phe Leu Ser Gly Glu Pro Ser Gln Ala Asp Val Gln Pro Leu Gly 2435 2440 2445 Pro Ser Ser Leu Ala Val His Thr Ile Leu Pro Gln Glu Ser Pro Ala 2450 2455 2460 Leu Pro Thr Ser Leu Pro Ser Ser Leu Val Pro Pro Val Thr Ala Ala 2465 2470 2475 2480 Gln Phe Leu Thr Pro Pro Ser Gln His Ser Tyr Ser Ser Pro Val Glu 2485 2490 2495 Asn Thr Pro Ser His Gln Leu Gln Val Pro Glu His Pro Phe Leu Thr 2500 2505 2510 Pro Ser Pro Glu Ser Pro Asp Gln Trp Ser Ser Ser Ser Pro His Ser 2515 2520 2525 Asn Val Ser Asp Trp Ser Glu Gly Val Ser Ser Pro Pro Thr Ser Met 2530 2535 2540 Gln Ser Gln Ile Ala Arg Ile Pro Glu Ala Phe Lys 2545 2550 2555 3 2523 PRT Xenopus sp. 3 Met Asp Arg Ile Gly Leu Ala Val Leu Leu Cys Ser Leu Pro Val Leu 1 5 10 15 Thr Gln Gly Leu Arg Cys Thr Gln Thr Ala Glu Met Cys Leu Asn Gly 20 25 30 Gly Arg Cys Glu Met Thr Pro Gly Gly Thr Gly Val Cys Leu Cys Gly 35 40 45 Asn Leu Tyr Phe Gly Glu Arg Cys Gln Phe Pro Asn Pro Cys Thr Ile 50 55 60 Lys Asn Gln Cys Met Asn Phe Gly Thr Cys Glu Pro Val Leu Gln Gly 65 70 75 80 Asn Ala Ile Asp Phe Ile Cys His Cys Pro Val Gly Phe Thr Asp Lys 85 90 95 Val Cys Leu Thr Pro Val Asp Asn Ala Cys Val Asn Asn Pro Cys Arg 100 105 110 Asn Gly Gly Thr Cys Glu Leu Leu Asn Ser Val Thr Glu Tyr Lys Cys 115 120 125 Arg Cys Pro Pro Gly Trp Thr Gly Asp Ser Cys Gln Gln Ala Asp Pro 130 135 140 Cys Ala Ser Asn Pro Cys Ala Asn Gly Gly Lys Cys Leu Pro Phe Glu 145 150 155 160 Ile Gln Tyr Ile Cys Lys Cys Pro Pro Gly Phe His Gly Ala Thr Cys 165 170 175 Lys Gln Asp Ile Asn Glu Cys Ser Gln Asn Pro Cys Lys Asn Gly Gly 180 185 190 Gln Cys Ile Asn Glu Phe Gly Ser Tyr Arg Cys Thr Cys Gln Asn Arg 195 200 205 Phe Thr Gly Arg Asn Cys Asp Glu Pro Tyr Val Pro Cys Asn Pro Ser 210 215 220 Pro Cys Leu Asn Gly Gly Thr Cys Arg Gln Thr Asp Asp Thr Ser Tyr 225 230 235 240 Asp Cys Thr Cys Leu Pro Gly Phe Ser Gly Gln Asn Cys Glu Glu Asn 245 250 255 Ile Asp Asp Cys Pro Ser Asn Asn Cys Arg Asn Gly Gly Thr Cys Val 260 265 270 Asp Gly Val Asn Thr Tyr Asn Cys Gln Cys Pro Pro Asp Trp Thr Gly 275 280 285 Gln Tyr Cys Thr Glu Asp Val Asp Glu Cys Gln Leu Met Pro Asn Ala 290 295 300 Cys Gln Asn Gly Gly Thr Cys His Asn Thr Tyr Gly Gly Tyr Asn Cys 305 310 315 320 Val Cys Val Asn Gly Trp Thr Gly Glu Asp Cys Ser Glu Asn Ile Asp 325 330 335 Asp Cys Ala Asn Ala Ala Cys His Ser Gly Ala Thr Cys His Asp Arg 340 345 350 Val Ala Ser Phe Tyr Cys Glu Cys Pro His Gly Arg Thr Gly Leu Leu 355 360 365 Cys His Leu Asp Asn Ala Cys Ile Ser Asn Pro Cys Asn Glu Gly Ser 370 375 380 Asn Cys Asp Thr Asn Pro Val Asn Gly Lys Ala Ile Cys Thr Cys Pro 385 390 395 400 Pro Gly Tyr Thr Gly Pro Ala Cys Asn Asn Asp Val Asp Glu Cys Ser 405 410 415 Leu Gly Ala Asn Pro Cys Glu His Gly Gly Arg Cys Thr Asn Thr Leu 420 425 430 Gly Ser Phe Gln Cys Asn Cys Pro Gln Gly Tyr Ala Gly Pro Arg Cys 435 440 445 Glu Ile Asp Val Asn Glu Cys Leu Ser Asn Pro Cys Gln Asn Asp Ser 450 455 460 Thr Cys Leu Asp Gln Ile Gly Glu Phe Gln Cys Ile Cys Met Pro Gly 465 470 475 480 Tyr Glu Gly Leu Tyr Cys Glu Thr Asn Ile Asp Glu Cys Ala Ser Asn 485 490 495 Pro Cys Leu His Asn Gly Lys Cys Ile Asp Lys Ile Asn Glu Phe Arg 500 505 510 Cys Asp Cys Pro Thr Gly Phe Ser Gly Asn Leu Cys Gln His Asp Phe 515 520 525 Asp Glu Cys Thr Ser Thr Pro Cys Lys Asn Gly Ala Lys Cys Leu Asp 530 535 540 Gly Pro Asn Ser Tyr Thr Cys Gln Cys Thr Glu Gly Phe Thr Gly Arg 545 550 555 560 His Cys Glu Gln Asp Ile Asn Glu Cys Ile Pro Asp Pro Cys His Tyr 565 570 575 Gly Thr Cys Lys Asp Gly Ile Ala Thr Phe Thr Cys Leu Cys Arg Pro 580 585 590 Gly Tyr Thr Gly Arg Leu Cys Asp Asn Asp Ile Asn Glu Cys Leu Ser 595 600 605 Lys Pro Cys Leu Asn Gly Gly Gln Cys Thr Asp Arg Glu Asn Gly Tyr 610 615 620 Ile Cys Thr Cys Pro Lys Gly Thr Thr Gly Val Asn Cys Glu Thr Lys 625 630 635 640 Ile Asp Asp Cys Ala Ser Asn Leu Cys Asp Asn Gly Lys Cys Ile Asp 645 650 655 Lys Ile Asp Gly Tyr Glu Cys Thr Cys Glu Pro Gly Tyr Thr Gly Lys 660 665 670 Leu Cys Asn Ile Asn Ile Asn Glu Cys Asp Ser Asn Pro Cys Arg Asn 675 680 685 Gly Gly Thr Cys Lys Asp Gln Ile Asn Gly Phe Thr Cys Val Cys Pro 690 695 700 Asp Gly Tyr His Asp His Met Cys Leu Ser Glu Val Asn Glu Cys Asn 705 710 715 720 Ser Asn Pro Cys Ile His Gly Ala Cys His Asp Gly Val Asn Gly Tyr 725 730 735 Lys Cys Asp Cys Glu Ala Gly Trp Ser Gly Ser Asn Cys Asp Ile Asn 740 745 750 Asn Asn Glu Cys Glu Ser Asn Pro Cys Met Asn Gly Gly Thr Cys Lys 755 760 765 Asp Met Thr Gly Ala Tyr Ile Cys Thr Cys Lys Ala Gly Phe Ser Gly 770 775 780 Pro Asn Cys Gln Thr Asn Ile Asn Glu Cys Ser Ser Asn Pro Cys Leu 785 790 795 800 Asn His Gly Thr Cys Ile Asp Asp Val Ala Gly Tyr Lys Cys Asn Cys 805 810 815 Met Leu Pro Tyr Thr Gly Ala Ile Cys Glu Ala Val Leu Ala Pro Cys 820 825 830 Ala Gly Ser Pro Cys Lys Asn Gly Gly Arg Cys Lys Glu Ser Glu Asp 835 840 845 Phe Glu Thr Phe Ser Cys Glu Cys Pro Pro Gly Trp Gln Gly Gln Thr 850 855 860 Cys Glu Ile Asp Met Asn Glu Cys Val Asn Arg Pro Cys Arg Asn Gly 865 870 875 880 Ala Thr Cys Gln Asn Thr Asn Gly Ser Tyr Lys Cys Asn Cys Lys Pro 885 890 895 Gly Tyr Thr Gly Arg Asn Cys Glu Met Asp Ile Asp Asp Cys Gln Pro 900 905 910 Asn Pro Cys His Asn Gly Gly Ser Cys Ser Asp Gly Ile Asn Met Phe 915 920 925 Phe Cys Asn Cys Pro Ala Gly Phe Arg Gly Pro Lys Cys Glu Glu Asp 930 935 940 Ile Asn Glu Cys Ala Ser Asn Pro Cys Lys Asn Gly Ala Asn Cys Thr 945 950 955 960 Asp Cys Val Asn Ser Tyr Thr Cys Thr Cys Gln Pro Gly Phe Ser Gly 965 970 975 Ile His Cys Glu Ser Asn Thr Pro Asp Cys Thr Glu Ser Ser Cys Phe 980 985 990 Asn Gly Gly Thr Cys Ile Asp Gly Ile Asn Thr Phe Thr Cys Gln Cys 995 1000 1005 Pro Pro Gly Phe Thr Gly Ser Tyr Cys Gln His Asp Ile Asn Glu Cys 1010 1015 1020 Asp Ser Lys Pro Cys Leu Asn Gly Gly Thr Cys Gln Asp Ser Tyr Gly 1025 1030 1035 1040 Thr Tyr Lys Cys Thr Cys Pro Gln Gly Tyr Thr Gly Leu Asn Cys Gln 1045 1050 1055 Asn Leu Val Arg Trp Cys Asp Ser Ser Pro Cys Lys Asn Gly Gly Lys 1060 1065 1070 Cys Trp Gln Thr Asn Asn Phe Tyr Arg Cys Glu Cys Lys Ser Gly Trp 1075 1080 1085 Thr Gly Val Tyr Cys Asp Val Pro Ser Val Ser Cys Glu Val Ala Ala 1090 1095 1100 Lys Gln Gln Gly Val Asp Ile Val His Leu Cys Arg Asn Ser Gly Met 1105 1110 1115 1120 Cys Val Asp Thr Gly Asn Thr His Phe Cys Arg Cys Gln Ala Gly Tyr 1125 1130 1135 Thr Gly Ser Tyr Cys Glu Glu Gln Val Asp Glu Cys Ser Pro Asn Pro 1140 1145 1150 Cys Gln Asn Gly Ala Thr Cys Thr Asp Tyr Leu Gly Gly Tyr Ser Cys 1155 1160 1165 Glu Cys Val Ala Gly Tyr His Gly Val Asn Cys Ser Glu Glu Ile Asn 1170 1175 1180 Glu Cys Leu Ser His Pro Cys Gln Asn Gly Gly Thr Cys Ile Asp Leu 1185 1190 1195 1200 Ile Asn Thr Tyr Lys Cys Ser Cys Pro Arg Gly Thr Gln Gly Val His 1205 1210 1215 Cys Glu Ile Asn Val Asp Asp Cys Thr Pro Phe Tyr Asp Ser Phe Thr 1220 1225 1230 Leu Glu Pro Lys Cys Phe Asn Asn Gly Lys Cys Ile Asp Arg Val Gly 1235 1240 1245 Gly Tyr Asn Cys Ile Cys Pro Pro Gly Phe Val Gly Glu Arg Cys Glu 1250 1255 1260 Gly Asp Val Asn Glu Cys Leu Ser Asn Pro Cys Asp Ser Arg Gly Thr 1265 1270 1275 1280 Gln Asn Cys Ile Gln Leu Val Asn Asp Tyr Arg Cys Glu Cys Arg Gln 1285 1290 1295 Gly Phe Thr Gly Arg Arg Cys Glu Ser Val Val Asp Gly Cys Lys Gly 1300 1305 1310 Met Pro Cys Arg Asn Gly Gly Thr Cys Ala Val Ala Ser Asn Thr Glu 1315 1320 1325 Arg Gly Phe Ile Cys Lys Cys Pro Pro Gly Phe Asp Gly Ala Thr Cys 1330 1335 1340 Glu Tyr Asp Ser Arg Thr Cys Ser Asn Leu Arg Cys Gln Asn Gly Gly 1345 1350 1355 1360 Thr Cys Ile Ser Val Leu Thr Ser Ser Lys Cys Val Cys Ser Glu Gly 1365 1370 1375 Tyr Thr Gly Ala Thr Cys Gln Tyr Pro Val Ile Ser Pro Cys Ala Ser 1380 1385 1390 His Pro Cys Tyr Asn Gly Gly Thr Cys Gln Phe Phe Ala Glu Glu Pro 1395 1400 1405 Phe Phe Gln Cys Phe Cys Pro Lys Asn Phe Asn Gly Leu Phe Cys His 1410 1415 1420 Ile Leu Asp Tyr Glu Phe Pro Gly Gly Leu Gly Lys Asn Ile Thr Pro 1425 1430 1435 1440 Pro Asp Asn Asp Asp Ile Cys Glu Asn Glu Gln Cys Ser Glu Leu Ala 1445 1450 1455 Asp Asn Lys Val Cys Asn Ala Asn Cys Asn Asn His Ala Cys Gly Trp 1460 1465 1470 Asp Gly Gly Asp Cys Ser Leu Asn Phe Asn Asp Pro Trp Lys Asn Cys 1475 1480 1485 Thr Gln Ser Leu Gln Cys Trp Lys Tyr Phe Asn Asp Gly Lys Cys Asp 1490 1495 1500 Ser Gln Cys Asn Asn Thr Gly Cys Leu Tyr Asp Gly Phe Asp Cys Gln 1505 1510 1515 1520 Lys Val Glu Val Gln Cys Asn Pro Leu Tyr Asp Gln Tyr Cys Lys Asp 1525 1530 1535 His Phe Gln Asp Gly His Cys Asp Gln Gly Cys Asn Asn Ala Glu Cys 1540 1545 1550 Glu Trp Asp Gly Leu Asp Cys Ala Asn Met Pro Glu Asn Leu Ala Glu 1555 1560 1565 Gly Thr Leu Val Leu Val Val Leu Met Pro Pro Glu Arg Leu Lys Asn 1570 1575 1580 Asn Ser Val Asn Phe Leu Arg Glu Leu Ser Arg Val Leu His Thr Asn 1585 1590 1595 1600 Val Val Phe Lys Lys Asp Ser Lys Gly Glu Tyr Lys Ile Tyr Pro Tyr 1605 1610 1615 Tyr Gly Asn Glu Glu Glu Leu Lys Lys His His Ile Lys Arg Ser Thr 1620 1625 1630 Asp Tyr Trp Ser Asp Ala Pro Ser Ala Ile Phe Ser Thr Met Lys Glu 1635 1640 1645 Ser Ile Leu Leu Gly Arg His Arg Arg Glu Leu Asp Glu Met Glu Val 1650 1655 1660 Arg Gly Ser Ile Val Tyr Leu Glu Ile Asp Asn Arg Gln Cys Tyr Lys 1665 1670 1675 1680 Ser Ser Ser Gln Cys Phe Asn Ser Ala Thr Asp Val Ala Ala Phe Leu 1685 1690 1695 Gly Ala Leu Ala Ser Leu Gly Ser Leu Asp Thr Leu Ser Tyr Lys Ile 1700 1705 1710 Glu Ala Val Lys Ser Glu Asn Met Glu Thr Pro Lys Pro Ser Thr Leu 1715 1720 1725 Tyr Pro Met Leu Ser Met Leu Val Ile Pro Leu Leu Ile Ile Phe Val 1730 1735 1740 Phe Met Met Val Ile Val Asn Lys Lys Arg Arg Arg Glu His Asp Ser 1745 1750 1755 1760 Phe Gly Ser Pro Thr Ala Leu Phe Gln Lys Asn Pro Ala Lys Arg Asn 1765 1770 1775 Gly Glu Thr Pro Trp Glu Asp Ser Val Gly Leu Lys Pro Ile Lys Asn 1780 1785 1790 Met Thr Asp Gly Ser Phe Met Asp Asp Asn Gln Asn Glu Trp Gly Asp 1795 1800 1805 Glu Glu Thr Leu Glu Asn Lys Arg Phe Arg Phe Glu Glu Gln Val Ile 1810 1815 1820 Leu Pro Glu Leu Val Asp Asp Lys Thr Asp Pro Arg Gln Trp Thr Arg 1825 1830 1835 1840 Gln His Leu Asp Ala Ala Asp Leu Arg Ile Ser Ser Met Ala Pro Thr 1845 1850 1855 Pro Pro Gln Gly Glu Ile Glu Ala Asp Cys Met Asp Val Asn Val Arg 1860 1865 1870 Gly Pro Asp Gly Phe Thr Pro Leu Met Ile Ala Ser Cys Ser Gly Gly 1875 1880 1885 Gly Leu Glu Thr Gly Asn Ser Glu Glu Glu Glu Asp Ala Ser Ala Asn 1890 1895 1900 Met Ile Ser Asp Phe Ile Gly Gln Gly Ala Gln Leu His Asn Gln Thr 1905 1910 1915 1920 Asp Arg Thr Gly Glu Thr Ala Leu His Leu Ala Ala Arg Tyr Ala Arg 1925 1930 1935 Ala Asp Ala Ala Lys Arg Leu Leu Glu Ser Ser Ala Asp Ala Asn Val 1940 1945 1950 Gln Asp Asn Met Gly Arg Thr Pro Leu His Ala Ala Val Ala Ala Asp 1955 1960 1965 Ala Gln Gly Val Phe Gln Ile Leu Ile Arg Asn Arg Ala Thr Asp Leu 1970 1975 1980 Asp Ala Arg Met Phe Asp Gly Thr Thr Pro Leu Ile Leu Ala Ala Arg 1985 1990 1995 2000 Leu Ala Val Glu Gly Met Val Glu Glu Leu Ile Asn Ala His Ala Asp 2005 2010 2015 Val Asn Ala Val Asp Glu Phe Gly Lys Ser Ala Leu His Trp Ala Ala 2020 2025 2030 Ala Val Asn Asn Val Asp Ala Ala Ala Val Leu Leu Lys Asn Ser Ala 2035 2040 2045 Asn Lys Asp Met Gln Asn Asn Lys Glu Glu Thr Ser Leu Phe Leu Ala 2050 2055 2060 Ala Arg Glu Gly Ser Tyr Glu Thr Ala Lys Val Leu Leu Asp His Tyr 2065 2070 2075 2080 Ala Asn Arg Asp Ile Thr Asp His Met Asp Arg Leu Pro Arg Asp Ile 2085 2090 2095 Ala Gln Glu Arg Met His His Asp Ile Val His Leu Leu Asp Glu Tyr 2100 2105 2110 Asn Leu Val Lys Ser Pro Thr Leu His Asn Gly Pro Leu Gly Ala Thr 2115 2120 2125 Thr Leu Ser Pro Pro Ile Cys Ser Pro Asn Gly Tyr Met Gly Asn Met 2130 2135 2140 Lys Pro Ser Val Gln Ser Lys Lys Ala Arg Lys Pro Ser Ile Lys Gly 2145 2150 2155 2160 Asn Gly Cys Lys Glu Ala Lys Glu Leu Lys Ala Arg Arg Lys Lys Ser 2165 2170 2175 Gln Asp Gly Lys Thr Thr Leu Leu Asp Ser Gly Ser Ser Gly Val Leu 2180 2185 2190 Ser Pro Val Asp Ser Leu Glu Ser Thr His Gly Tyr Leu Ser Asp Val 2195 2200 2205 Ser Ser Pro Pro Leu Met Thr Ser Pro Phe Gln Gln Ser Pro Ser Met 2210 2215 2220 Pro Leu Asn His Leu Thr Ser Met Pro Glu Ser Gln Leu Gly Met Asn 2225 2230 2235 2240 His Ile Asn Met Ala Thr Lys Gln Glu Met Ala Ala Gly Ser Asn Arg 2245 2250 2255 Met Ala Phe Asp Ala Met Val Pro Arg Leu Thr His Leu Asn Ala Ser 2260 2265 2270 Ser Pro Asn Thr Ile Met Ser Asn Gly Ser Met His Phe Thr Val Gly 2275 2280 2285 Gly Ala Pro Thr Met Asn Ser Gln Cys Asp Trp Leu Ala Arg Leu Gln 2290 2295 2300 Asn Gly Met Val Gln Asn Gln Tyr Asp Pro Ile Arg Asn Gly Ile Gln 2305 2310 2315 2320 Gln Gly Asn Ala Gln Gln Ala Gln Ala Leu Gln His Gly Leu Met Thr 2325 2330 2335 Ser Leu His Asn Gly Leu Pro Ala Thr Thr Leu Ser Gln Met Met Thr 2340 2345 2350 Tyr Gln Ala Met Pro Asn Thr Arg Leu Ala Asn Gln Pro His Leu Met 2355 2360 2365 Gln Ala Gln Gln Met Gln Gln Gln Gln Asn Leu Gln Leu His Gln Ser 2370 2375 2380 Met Gln Gln Gln His His Asn Ser Ser Thr Thr Ser Thr His Ile Asn 2385 2390 2395 2400 Ser Pro Phe Cys Ser Ser Asp Ile Ser Gln Thr Asp Leu Gln Gln Met 2405 2410 2415 Ser Ser Asn Asn Ile His Ser Val Met Pro Gln Asp Thr Gln Ile Phe 2420 2425 2430 Ala Ala Ser Leu Pro Ser Asn Leu Thr Gln Ser Met Thr Thr Ala Gln 2435 2440 2445 Phe Leu Thr Pro Pro Ser Gln His Ser Tyr Ser Ser Pro Met Asp Asn 2450 2455 2460 Thr Pro Ser His Gln Leu Gln Val Pro Asp His Pro Phe Leu Thr Pro 2465 2470 2475 2480 Ser Pro Glu Ser Pro Asp Gln Trp Ser Ser Ser Ser Pro His Ser Asn 2485 2490 2495 Met Ser Asp Trp Ser Glu Gly Ile Ser Ser Pro Pro Thr Ser Met Gln 2500 2505 2510 Pro Gln Arg Thr His Ile Pro Glu Ala Phe Lys 2515 2520 4 2703 PRT Drosophila sp. 4 Met Gln Ser Gln Arg Ser Arg Arg Arg Ser Arg Ala Pro Asn Thr Trp 1 5 10 15 Ile Cys Phe Trp Ile Asn Lys Met His Ala Val Ala Ser Leu Pro Ala 20 25 30 Ser Leu Pro Leu Leu Leu Leu Thr Leu Ala Phe Ala Asn Leu Pro Asn 35 40 45 Ile Val Arg Gly Thr Asp Thr Ala Leu Val Ala Ala Ser Cys Thr Ser 50 55 60 Val Gly Cys Gln Asn Gly Gly Thr Cys Val Thr Gln Leu Asn Gly Lys 65 70 75 80 Thr Tyr Cys Ala Cys Asp Ser His Tyr Val Gly Asp Tyr Cys Glu His 85 90 95 Arg Asn Pro Cys Asn Ser Met Arg Cys Gln Asn Gly Gly Thr Cys Gln 100 105 110 Val Thr Phe Arg Asn Gly Arg Pro Gly Ile Ser Cys Lys Cys Pro Leu 115 120 125 Gly Phe Asp Glu Ser Leu Cys Glu Ile Ala Val Pro Asn Ala Cys Asp 130 135 140 His Val Thr Cys Leu Asn Gly Gly Thr Cys Gln Leu Lys Thr Leu Glu 145 150 155 160 Glu Tyr Thr Cys Ala Cys Ala Asn Gly Tyr Thr Gly Glu Arg Cys Glu 165 170 175 Thr Lys Asn Leu Cys Ala Ser Ser Pro Cys Arg Asn Gly Ala Thr Cys 180 185 190 Thr Ala Leu Ala Gly Ser Ser Ser Phe Thr Cys Ser Cys Pro Pro Gly 195 200 205 Phe Thr Gly Asp Thr Cys Ser Tyr Asp Ile Glu Glu Cys Gln Ser Asn 210 215 220 Pro Cys Lys Tyr Gly Gly Ile Cys Val Asn Thr His Gly Ser Tyr Gln 225 230 235 240 Cys Met Cys Pro Thr Gly Tyr Thr Gly Lys Asp Cys Asp Thr Lys Tyr 245 250 255 Lys Pro Cys Ser Pro Ser Pro Cys Gln Asn Ala Gly Ile Cys Arg Ser 260 265 270 Asn Gly Leu Ser Tyr Glu Cys Lys Cys Pro Lys Gly Phe Glu Gly Lys 275 280 285 Asn Cys Glu Gln Asn Tyr Asp Asp Cys Leu Gly His Leu Cys Gln Asn 290 295 300 Gly Gly Thr Cys Ile Asp Gly Ile Ser Asp Tyr Thr Cys Arg Cys Pro 305 310 315 320 Pro Asn Phe Thr Gly Arg Phe Cys Gln Asp Asp Val Asp Glu Cys Ala 325 330 335 Gln Arg Asp His Pro Val Cys Gln Asn Gly Ala Thr Cys Thr Asn Thr 340 345 350 His Gly Ser Tyr Ser Cys Ile Cys Val Asn Gly Trp Ala Gly Leu Asp 355 360 365 Cys Ser Asn Asn Thr Asp Asp Cys Lys Gln Ala Ala Cys Phe Tyr Gly 370 375 380 Ala Thr Cys Ile Asp Gly Val Gly Ser Phe Tyr Cys Gln Cys Thr Lys 385 390 395 400 Gly Lys Thr Gly Leu Leu Cys His Leu Asp Asp Ala Cys Thr Ser Asn 405 410 415 Pro Cys His Ala Asp Ala Ile Cys Asp Thr Ser Pro Ile Asn Gly Ser 420 425 430 Tyr Ala Cys Ser Cys Ala Thr Gly Tyr Lys Gly Val Asp Cys Ser Glu 435 440 445 Asp Ile Asp Glu Cys Asp Gln Gly Ser Pro Cys Glu His Asn Gly Ile 450 455 460 Cys Val Asn Thr Pro Gly Ser Tyr Arg Cys Asn Cys Ser Gln Gly Phe 465 470 475 480 Thr Gly Pro Arg Cys Glu Thr Asn Ile Asn Glu Cys Glu Ser His Pro 485 490 495 Cys Gln Asn Glu Gly Ser Cys Leu Asp Asp Pro Gly Thr Phe Arg Cys 500 505 510 Val Cys Met Pro Gly Phe Thr Gly Thr Gln Cys Glu Ile Asp Ile Asp 515 520 525 Glu Cys Gln Ser Asn Pro Cys Leu Asn Asp Gly Thr Cys His Asp Lys 530 535 540 Ile Asn Gly Phe Lys Cys Ser Cys Ala Leu Gly Phe Thr Gly Ala Arg 545 550 555 560 Cys Gln Ile Asn Ile Asp Asp Cys Gln Ser Gln Pro Cys Arg Asn Arg 565 570 575 Gly Ile Cys His Asp Ser Ile Ala Gly Tyr Ser Cys Glu Cys Pro Pro 580 585 590 Gly Tyr Thr Gly Thr Ser Cys Glu Ile Asn Ile Asn Asp Cys Asp Ser 595 600 605 Asn Pro Cys His Arg Gly Lys Cys Ile Asp Asp Val Asn Ser Phe Lys 610 615 620 Cys Leu Cys Asp Pro Gly Tyr Thr Gly Tyr Ile Cys Gln Lys Gln Ile 625 630 635 640 Asn Glu Cys Glu Ser Asn Pro Cys Gln Phe Asp Gly His Cys Gln Asp 645 650 655 Arg Val Gly Ser Tyr Tyr Cys Gln Cys Gln Ala Gly Thr Ser Gly Lys 660 665 670 Asn Cys Glu Val Asn Val Asn Glu Cys His Ser Asn Pro Cys Asn Asn 675 680 685 Gly Ala Thr Cys Ile Asp Gly Ile Asn Ser Tyr Lys Cys Gln Cys Val 690 695 700 Pro Gly Phe Thr Gly Gln His Cys Glu Lys Asn Val Asp Glu Cys Ile 705 710 715 720 Ser Ser Pro Cys Ala Asn Asn Gly Val Cys Ile Asp Gln Val Asn Gly 725 730 735 Tyr Lys Cys Glu Cys Pro Arg Gly Phe Tyr Asp Ala His Cys Leu Ser 740 745 750 Asp Val Asp Glu Cys Ala Ser Asn Pro Cys Val Asn Glu Gly Arg Cys 755 760 765 Glu Asp Gly Ile Asn Glu Phe Ile Cys His Cys Pro Pro Gly Tyr Thr 770 775 780 Gly Lys Arg Cys Glu Leu Asp Ile Asp Glu Cys Ser Ser Asn Pro Cys 785 790 795 800 Gln His Gly Gly Thr Cys Tyr Asp Lys Leu Asn Ala Phe Ser Cys Gln 805 810 815 Cys Met Pro Gly Tyr Thr Gly Gln Lys Cys Glu Thr Asn Ile Asp Asp 820 825 830 Cys Val Thr Asn Pro Cys Gly Asn Gly Gly Thr Cys Ile Asp Lys Val 835 840 845 Asn Gly Tyr Lys Cys Val Cys Lys Val Pro Phe Thr Gly Arg Asp Cys 850 855 860 Glu Ser Lys Met Asp Pro Cys Ala Arg Asn Arg Cys Lys Asn Glu Ala 865 870 875 880 Lys Cys Thr Pro Ser Ser Asn Phe Leu Asp Phe Ser Cys Thr Cys Lys 885 890 895 Leu Gly Tyr Thr Gly Arg Tyr Cys Asp Glu Asp Ile Asp Glu Cys Ser 900 905 910 Leu Ser Ser Pro Cys Arg Asn Gly Ala Ser Cys Leu Asn Val Pro Gly 915 920 925 Ser Tyr Arg Cys Leu Cys Thr Lys Gly Tyr Glu Gly Arg Asp Cys Ala 930 935 940 Ile Asn Thr Asp Asp Cys Ala Ser Phe Pro Cys Gln Asn Gly Arg Thr 945 950 955 960 Cys Leu Asp Gly Ile Gly Asp Tyr Ser Cys Leu Cys Val Asp Gly Phe 965 970 975 Asp Gly Lys His Cys Glu Thr Asp Ile Asn Glu Cys Leu Ser Gln Pro 980 985 990 Cys Gln Asn Gly Ala Thr Cys Ser Gln Tyr Val Asn Ser Tyr Thr Cys 995 1000 1005 Thr Cys Pro Leu Gly Phe Ser Gly Ile Asn Cys Gln Thr Asn Asp Glu 1010 1015 1020 Asp Cys Thr Glu Ser Ser Cys Leu Asn Gly Gly Ser Cys Ile Asp Gly 1025 1030 1035 1040 Ile Asn Gly Tyr Asn Cys Ser Cys Leu Ala Gly Tyr Ser Gly Ala Asn 1045 1050 1055 Cys Gln Tyr Lys Leu Asn Lys Cys Asp Ser Asn Pro Cys Leu Asn Gly 1060 1065 1070 Ala Thr Cys His Glu Gln Asn Asn Glu Tyr Thr Cys His Cys Pro Ser 1075 1080 1085 Gly Phe Thr Gly Lys Gln Cys Ser Glu Tyr Val Asp Trp Cys Gly Gln 1090 1095 1100 Ser Pro Cys Glu Asn Gly Ala Thr Cys Ser Gln Met Lys His Gln Phe 1105 1110 1115 1120 Ser Cys Lys Cys Ser Ala Gly Trp Thr Gly Lys Leu Cys Asp Val Gln 1125 1130 1135 Thr Ile Ser Cys Gln Asp Ala Ala Asp Arg Lys Gly Leu Ser Leu Arg 1140 1145 1150 Gln Leu Cys Asn Asn Gly Thr Cys Lys Asp Tyr Gly Asn Ser His Val 1155 1160 1165 Cys Tyr Cys Ser Gln Gly Tyr Ala Gly Ser Tyr Cys Gln Lys Glu Ile 1170 1175 1180 Asp Glu Cys Gln Ser Gln Pro Cys Gln Asn Gly Gly Thr Cys Arg Asp 1185 1190 1195 1200 Leu Ile Gly Ala Tyr Glu Cys Gln Cys Arg Gln Gly Phe Gln Gly Gln 1205 1210 1215 Asn Cys Glu Leu Asn Ile Asp Asp Cys Ala Pro Asn Pro Cys Gln Asn 1220 1225 1230 Gly Gly Thr Cys His Asp Arg Val Met Asn Phe Ser Cys Ser Cys Pro 1235 1240 1245 Pro Gly Thr Met Gly Ile Ile Cys Glu Ile Asn Lys Asp Asp Cys Lys 1250 1255 1260 Pro Gly Ala Cys His Asn Asn Gly Ser Cys Ile Asp Arg Val Gly Gly 1265 1270 1275 1280 Phe Glu Cys Val Cys Gln Pro Gly Phe Val Gly Ala Arg Cys Glu Gly 1285 1290 1295 Asp Ile Asn Glu Cys Leu Ser Asn Pro Cys Ser Asn Ala Gly Thr Leu 1300 1305 1310 Asp Cys Val Gln Leu Val Asn Asn Tyr His Cys Asn Cys Arg Pro Gly 1315 1320 1325 His Met Gly Arg His Cys Glu His Lys Val Asp Phe Cys Ala Gln Ser 1330 1335 1340 Pro Cys Gln Asn Gly Gly Asn Cys Asn Ile Arg Gln Ser Gly His His 1345 1350 1355 1360 Cys Ile Cys Asn Asn Gly Phe Tyr Gly Lys Asn Cys Glu Leu Ser Gly 1365 1370 1375 Gln Asp Cys Asp Ser Asn Pro Cys Arg Val Gly Asn Cys Val Val Ala 1380 1385 1390 Asp Glu Gly Phe Gly Tyr Arg Cys Glu Cys Pro Arg Gly Thr Leu Gly 1395 1400 1405 Glu His Cys Glu Ile Asp Thr Leu Asp Glu Cys Ser Pro Asn Pro Cys 1410 1415 1420 Ala Gln Gly Ala Ala Cys Glu Asp Leu Leu Gly Asp Tyr Glu Cys Leu 1425 1430 1435 1440 Cys Pro Ser Lys Trp Lys Gly Lys Arg Cys Asp Ile Tyr Asp Ala Asn 1445 1450 1455 Tyr Pro Gly Trp Asn Gly Gly Ser Gly Ser Gly Asn Asp Arg Tyr Ala 1460 1465 1470 Ala Asp Leu Glu Gln Gln Arg Ala Met Cys Asp Lys Arg Gly Cys Thr 1475 1480 1485 Glu Lys Gln Gly Asn Gly Ile Cys Asp Ser Asp Cys Asn Thr Tyr Ala 1490 1495 1500 Cys Asn Phe Asp Gly Asn Asp Cys Ser Leu Gly Ile Asn Pro Trp Ala 1505 1510 1515 1520 Asn Cys Thr Ala Asn Glu Cys Trp Asn Lys Phe Lys Asn Gly Lys Cys 1525 1530 1535 Asn Glu Glu Cys Asn Asn Ala Ala Cys His Tyr Asp Gly His Asp Cys 1540 1545 1550 Glu Arg Lys Leu Lys Ser Cys Asp Thr Leu Phe Asp Ala Tyr Cys Gln 1555 1560 1565 Lys His Tyr Gly Asp Gly Phe Cys Asp Tyr Gly Cys Asn Asn Ala Glu 1570 1575 1580 Cys Ser Trp Asp Gly Leu Asp Cys Glu Asn Lys Thr Gln Ser Pro Val 1585 1590 1595 1600 Leu Ala Glu Gly Ala Met Ser Val Val Met Leu Met Asn Val Glu Ala 1605 1610 1615 Phe Arg Glu Ile Gln Ala Gln Phe Leu Arg Asn Met Ser His Met Leu 1620 1625 1630 Arg Thr Thr Val Arg Leu Lys Lys Asp Ala Leu Gly His Asp Ile Ile 1635 1640 1645 Ile Asn Trp Lys Asp Asn Val Arg Val Pro Glu Ile Glu Asp Thr Asp 1650 1655 1660 Phe Ala Arg Lys Asn Lys Ile Leu Tyr Thr Gln Gln Val His Gln Thr 1665 1670 1675 1680 Gly Ile Gln Ile Tyr Leu Glu Ile Asp Asn Arg Lys Cys Thr Glu Cys 1685 1690 1695 Phe Thr His Ala Val Glu Ala Ala Glu Phe Leu Ala Ala Thr Ala Ala 1700 1705 1710 Lys His Gln Leu Arg Asn Asp Phe Gln Ile His Ser Val Arg Gly Ile 1715 1720 1725 Lys Asn Pro Gly Asp Glu Asp Asn Gly Glu Pro Pro Ala Asn Val Lys 1730 1735 1740 Tyr Val Ile Thr Gly Ile Ile Leu Val Ile Ile Ala Leu Ala Phe Phe 1745 1750 1755 1760 Gly Met Val Leu Ser Thr Gln Arg Lys Arg Ala His Gly Val Thr Trp 1765 1770 1775 Phe Pro Glu Gly Phe Arg Ala Pro Ala Ala Val Met Ser Arg Arg Arg 1780 1785 1790 Arg Asp Pro His Gly Gln Glu Met Arg Asn Leu Asn Lys Gln Val Ala 1795 1800 1805 Met Gln Ser Gln Gly Val Gly Gln Pro Gly Ala His Trp Ser Asp Asp 1810 1815 1820 Glu Ser Asp Met Pro Leu Pro Lys Arg Gln Arg Ser Asp Pro Val Ser 1825 1830 1835 1840 Gly Val Gly Leu Gly Asn Asn Gly Gly Tyr Ala Ser Asp His Thr Met 1845 1850 1855 Val Ser Glu Tyr Glu Glu Ala Asp Gln Arg Val Trp Ser Gln Ala His 1860 1865 1870 Leu Asp Val Val Asp Val Arg Ala Ile Met Thr Pro Pro Ala His Gln 1875 1880 1885 Asp Gly Gly Lys His Asp Val Asp Ala Arg Gly Pro Cys Gly Leu Thr 1890 1895 1900 Pro Leu Met Ile Ala Ala Val Arg Gly Gly Gly Leu Asp Thr Gly Glu 1905 1910 1915 1920 Asp Ile Glu Asn Asn Glu Asp Ser Thr Ala Gln Val Ile Ser Asp Leu 1925 1930 1935 Leu Ala Gln Gly Ala Glu Leu Asn Ala Thr Met Asp Lys Thr Gly Glu 1940 1945 1950 Thr Ser Leu His Leu Ala Ala Arg Phe Ala Arg Ala Asp Ala Ala Lys 1955 1960 1965 Arg Leu Phe His Ala Gly Ala Asp Ala Asn Cys Gln Asp Asn Thr Gly 1970 1975 1980 Arg Thr Pro Leu His Ala Ala Val Ala Ala Asp Ala Met Gly Val Phe 1985 1990 1995 2000 Gln Ile Leu Leu Arg Asn Arg Ala Thr Asn Leu Asn Ala Arg Met His 2005 2010 2015 Asp Gly Thr Thr Pro Leu Ile Leu Ala Ala Arg Leu Ala Ile Glu Gly 2020 2025 2030 Met Val Glu Asp Leu Ile Thr Ala Asp Ala Asp Ile Asn Ala Ala Asp 2035 2040 2045 Asn Ser Gly Lys Thr Ala Leu His Trp Ala Ala Ala Val Asn Asn Thr 2050 2055 2060 Glu Ala Val Asn Ile Leu Leu Met His His Ala Asn Arg Asp Ala Gln 2065 2070 2075 2080 Asp Asp Lys Asp Glu Thr Pro Leu Phe Leu Ala Ala Arg Glu Gly Ser 2085 2090 2095 Tyr Glu Ala Cys Lys Ala Leu Leu Asp Asn Phe Ala Asn Arg Glu Ile 2100 2105 2110 Thr Asp His Met Asp Arg Leu Pro Arg Asp Val Ala Ser Glu Arg Leu 2115 2120 2125 His His Asp Ile Val Arg Leu Leu Asp Glu His Val Pro Arg Ser Pro 2130 2135 2140 Gln Met Leu Ser Met Thr Pro Gln Ala Met Ile Gly Ser Pro Pro Pro 2145 2150 2155 2160 Gly Gln Gln Gln Pro Gln Leu Ile Thr Gln Pro Thr Val Ile Ser Ala 2165 2170 2175 Gly Asn Gly Gly Asn Asn Gly Asn Gly Asn Ala Ser Gly Lys Gln Ser 2180 2185 2190 Asn Gln Thr Ala Lys Gln Lys Ala Ala Lys Lys Ala Lys Leu Ile Glu 2195 2200 2205 Gly Ser Pro Asp Asn Gly Leu Asp Ala Thr Gly Ser Leu Arg Arg Lys 2210 2215 2220 Ala Ser Ser Lys Lys Thr Ser Ala Ala Ser Lys Lys Ala Ala Asn Leu 2225 2230 2235 2240 Asn Gly Leu Asn Pro Gly Gln Leu Thr Gly Gly Val Ser Gly Val Pro 2245 2250 2255 Gly Val Pro Pro Thr Asn Ser Ala Val Gln Ala Ala Ala Ala Ala Ala 2260 2265 2270 Ala Ala Val Ala Ala Met Ser His Glu Leu Glu Gly Ser Pro Val Gly 2275 2280 2285 Val Gly Met Gly Gly Asn Leu Pro Ser Pro Tyr Asp Thr Ser Ser Met 2290 2295 2300 Tyr Ser Asn Ala Met Ala Ala Pro Leu Ala Asn Gly Asn Pro Asn Thr 2305 2310 2315 2320 Gly Ala Lys Gln Pro Pro Ser Tyr Glu Asp Cys Ile Lys Asn Ala Gln 2325 2330 2335 Ser Met Gln Ser Leu Gln Gly Asn Gly Leu Asp Met Ile Lys Leu Asp 2340 2345 2350 Asn Tyr Ala Tyr Ser Met Gly Ser Pro Phe Gln Gln Glu Leu Leu Asn 2355 2360 2365 Gly Gln Gly Leu Gly Met Asn Gly Asn Gly Gln Arg Asn Gly Val Gly 2370 2375 2380 Pro Gly Val Leu Pro Gly Gly Leu Cys Gly Met Gly Gly Leu Ser Gly 2385 2390 2395 2400 Ala Gly Asn Gly Asn Ser Arg Glu Gln Gly Leu Ser Pro Pro Tyr Ser 2405 2410 2415 Asn Gln Ser Pro Pro His Ser Val Gln Ser Ser Leu Ala Leu Ser Pro 2420 2425 2430 His Ala Tyr Leu Gly Ser Pro Ser Pro Ala Lys Ser Leu Pro Ser Leu 2435 2440 2445 Pro Thr Ser Pro Thr His Ile Gln Ala Met Arg His Ala Thr Gln Gln 2450 2455 2460 Lys Gln Phe Gly Gly Ser Asn Leu Asn Ser Leu Leu Gly Gly Ala Asn 2465 2470 2475 2480 Gly Gly Gly Val Val Gly Gly Gly Gly Gly Gly Gly Gly Gly Val Gly 2485 2490 2495 Gln Gly Pro Gln Asn Ser Pro Val Ser Leu Gly Ile Ile Ser Pro Thr 2500 2505 2510 Gly Ser Asp Met Gly Ile Met Leu Ala Pro Pro Gln Ser Ser Lys Asn 2515 2520 2525 Ser Ala Ile Met Gln Thr Ile Ser Pro Gln Gln Gln Gln Gln Gln Gln 2530 2535 2540 Gln Gln Gln Gln Gln Gln His Gln Gln Gln Gln Gln Gln Gln Gln Gln 2545 2550 2555 2560 Gln Gln Gln Gln Gln Gln Gln Gln Leu Gly Gly Leu Glu Phe Gly Ser 2565 2570 2575 Ala Gly Leu Asp Leu Asn Gly Phe Cys Gly Ser Pro Asp Ser Phe His 2580 2585 2590 Ser Gly Gln Met Asn Pro Pro Ser Ile Gln Ser Ser Met Ser Gly Ser 2595 2600 2605 Ser Pro Ser Thr Asn Met Leu Ser Pro Ser Ser Gln His Asn Gln Gln 2610 2615 2620 Ala Phe Tyr Gln Tyr Leu Thr Pro Ser Ser Gln His Ser Gly Gly His 2625 2630 2635 2640 Thr Pro Gln His Leu Val Gln Thr Leu Asp Ser Tyr Pro Thr Pro Ser 2645 2650 2655 Pro Glu Ser Pro Gly His Trp Ser Ser Ser Ser Pro Arg Ser Asn Ser 2660 2665 2670 Asp Trp Ser Glu Gly Val Gln Ser Pro Ala Ala Asn Asn Leu Tyr Ile 2675 2680 2685 Ser Gly Gly His Gln Ala Asn Lys Gly Ser Glu Ala Ile Tyr Ile 2690 2695 2700 

What is claimed is:
 1. A method for detecting or measuring the form of Notch that mediates Notch signal transduction in a sample of cells comprising detecting or measuring the expression of a Notch heterodimer containing a reducing agent-sensitive linkage on the surface of cells in said cell sample, in which the heterodimer consists of an amino-terminal fragment of full-length Notch terminating between the epidermal growth factor-like repeat domain and the transmembrane domain of full-length Notch, and a carboxy-terminal fragment of full-length Notch with its amino terminus situated between the epidermal growth factor-like repeat domain and the transmembrane domain, and comparing said detected or measured expression to the detected or measured expression of full length Notch in said cells, wherein the presence and amount of Notch on the surface of said cells compared to the presence and amount, respectively, of full length Notch in said cells indicates the relative presence and amount, respectively, of the form of Notch that mediates Notch signal transduction.
 2. The method according to claim 1 in which the amino-terminal fragment of full-length Notch terminates between the Lin-12/Notch repeats and the transmembrane domain, and the carboxy-terminal fragment of full-length Notch has its amino terminus situated between the Lin-12/Notch repeats and the transmembrane domain.
 3. The method according to claim 1 in which the reducing agent sensitive linkage is a non-covalent, metal ion-dependent sensitive linkage.
 4. The method according to claim 1 in which the heterodimer consists of N^(EC) and N^(TM).
 5. A method for detecting or measuring the form of Notch that mediates Notch signal transduction in a sample of cells comprising detecting or measuring the expression of a Notch heterodimer containing a reducing agent-sensitive linkage in said cells, and comparing said detected or measured expression of Notch heterodimer to the detected or measured expression of full length Notch in said cells, wherein the presence and amount of said Notch heterodimer compared to the presence and amount, respectively, of full length Notch in said cells indicates the relative presence and amount, respectively, of the form of Notch that mediates Notch signal transduction, in which the heterodimer consists of N^(EC) and N^(TM).
 6. The method according to claim 5 in which the reducing agent-sensitive linkage is a non-covalent, metal ion-dependent sensitive linkage. 